| Message ID | 20200610194101.1668038-1-daniel.vetter@ffwll.ch (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | mm: Track mmu notifiers in fs_reclaim_acquire/release | expand |
On Wed, Jun 10, 2020 at 09:41:01PM +0200, Daniel Vetter wrote: > fs_reclaim_acquire/release nicely catch recursion issues when > allocating GFP_KERNEL memory against shrinkers (which gpu drivers tend > to use to keep the excessive caches in check). For mmu notifier > recursions we do have lockdep annotations since 23b68395c7c7 > ("mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end"). > > But these only fire if a path actually results in some pte > invalidation - for most small allocations that's very rarely the case. > The other trouble is that pte invalidation can happen any time when > __GFP_RECLAIM is set. Which means only really GFP_ATOMIC is a safe > choice, GFP_NOIO isn't good enough to avoid potential mmu notifier > recursion. > > I was pondering whether we should just do the general annotation, but > there's always the risk for false positives. Plus I'm assuming that > the core fs and io code is a lot better reviewed and tested than > random mmu notifier code in drivers. Hence why I decide to only > annotate for that specific case. > > Furthermore even if we'd create a lockdep map for direct reclaim, we'd > still need to explicit pull in the mmu notifier map - there's a lot > more places that do pte invalidation than just direct reclaim, these > two contexts arent the same. > > Note that the mmu notifiers needing their own independent lockdep map > is also the reason we can't hold them from fs_reclaim_acquire to > fs_reclaim_release - it would nest with the acquistion in the pte > invalidation code, causing a lockdep splat. And we can't remove the > annotations from pte invalidation and all the other places since > they're called from many other places than page reclaim. Hence we can > only do the equivalent of might_lock, but on the raw lockdep map. > > With this we can also remove the lockdep priming added in 66204f1d2d1b > ("mm/mmu_notifiers: prime lockdep") since the new annotations are > strictly more powerful. > > v2: Review from Thomas Hellstrom: > - unbotch the fs_reclaim context check, I accidentally inverted it, > but it didn't blow up because I inverted it immediately > - fix compiling for !CONFIG_MMU_NOTIFIER > > Cc: Thomas Hellström (Intel) <thomas_os@shipmail.org> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Jason Gunthorpe <jgg@mellanox.com> > Cc: linux-mm@kvack.org > Cc: linux-rdma@vger.kernel.org > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> > Cc: Christian König <christian.koenig@amd.com> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> > --- > This is part of a gpu lockdep annotation series simply because it > really helps to catch issues where gpu subsystem locks and primitives > can deadlock with themselves through allocations and mmu notifiers. > But aside from that motivation it should be completely free-standing, > and can land through -mm/-rdma/-hmm or any other tree really whenever. > -Daniel I'm still not totally clear on how all the GFP flags map to different behaviors, but this seems plausible to me At this point it should go through Andrew's tree, thanks Acked-by: Jason Gunthorpe <jgg@mellanox.com> # For mmu_notifiers Jason
On Wed, Jun 10, 2020 at 09:41:01PM +0200, Daniel Vetter wrote: > fs_reclaim_acquire/release nicely catch recursion issues when > allocating GFP_KERNEL memory against shrinkers (which gpu drivers tend > to use to keep the excessive caches in check). For mmu notifier > recursions we do have lockdep annotations since 23b68395c7c7 > ("mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end"). > > But these only fire if a path actually results in some pte > invalidation - for most small allocations that's very rarely the case. > The other trouble is that pte invalidation can happen any time when > __GFP_RECLAIM is set. Which means only really GFP_ATOMIC is a safe > choice, GFP_NOIO isn't good enough to avoid potential mmu notifier > recursion. > > I was pondering whether we should just do the general annotation, but > there's always the risk for false positives. Plus I'm assuming that > the core fs and io code is a lot better reviewed and tested than > random mmu notifier code in drivers. Hence why I decide to only > annotate for that specific case. > > Furthermore even if we'd create a lockdep map for direct reclaim, we'd > still need to explicit pull in the mmu notifier map - there's a lot > more places that do pte invalidation than just direct reclaim, these > two contexts arent the same. > > Note that the mmu notifiers needing their own independent lockdep map > is also the reason we can't hold them from fs_reclaim_acquire to > fs_reclaim_release - it would nest with the acquistion in the pte > invalidation code, causing a lockdep splat. And we can't remove the > annotations from pte invalidation and all the other places since > they're called from many other places than page reclaim. Hence we can > only do the equivalent of might_lock, but on the raw lockdep map. > > With this we can also remove the lockdep priming added in 66204f1d2d1b > ("mm/mmu_notifiers: prime lockdep") since the new annotations are > strictly more powerful. > > v2: Review from Thomas Hellstrom: > - unbotch the fs_reclaim context check, I accidentally inverted it, > but it didn't blow up because I inverted it immediately > - fix compiling for !CONFIG_MMU_NOTIFIER > > Cc: Thomas Hellström (Intel) <thomas_os@shipmail.org> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Jason Gunthorpe <jgg@mellanox.com> > Cc: linux-mm@kvack.org > Cc: linux-rdma@vger.kernel.org > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> > Cc: Christian König <christian.koenig@amd.com> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> Replying the right patch here... Reverting this commit [1] fixed the lockdep warning below while applying some memory pressure. [1] linux-next cbf7c9d86d75 ("mm: track mmu notifiers in fs_reclaim_acquire/release") [ 190.455003][ T369] WARNING: possible circular locking dependency detected [ 190.487291][ T369] 5.8.0-rc1-next-20200621 #1 Not tainted [ 190.512363][ T369] ------------------------------------------------------ [ 190.543354][ T369] kswapd3/369 is trying to acquire lock: [ 190.568523][ T369] ffff889fcf694528 (&xfs_nondir_ilock_class){++++}-{3:3}, at: xfs_reclaim_inode+0xdf/0x860 spin_lock at include/linux/spinlock.h:353 (inlined by) xfs_iflags_test_and_set at fs/xfs/xfs_inode.h:166 (inlined by) xfs_iflock_nowait at fs/xfs/xfs_inode.h:249 (inlined by) xfs_reclaim_inode at fs/xfs/xfs_icache.c:1127 [ 190.614359][ T369] [ 190.614359][ T369] but task is already holding lock: [ 190.647763][ T369] ffffffffb50ced00 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x0/0x30 __fs_reclaim_acquire at mm/page_alloc.c:4200 [ 190.687845][ T369] [ 190.687845][ T369] which lock already depends on the new lock. [ 190.687845][ T369] [ 190.734890][ T369] [ 190.734890][ T369] the existing dependency chain (in reverse order) is: [ 190.775991][ T369] [ 190.775991][ T369] -> #1 (fs_reclaim){+.+.}-{0:0}: [ 190.808150][ T369] fs_reclaim_acquire+0x77/0x80 [ 190.832152][ T369] slab_pre_alloc_hook.constprop.52+0x20/0x120 slab_pre_alloc_hook at mm/slab.h:507 [ 190.862173][ T369] kmem_cache_alloc+0x43/0x2a0 [ 190.885602][ T369] kmem_zone_alloc+0x113/0x3ef kmem_zone_alloc at fs/xfs/kmem.c:129 [ 190.908702][ T369] xfs_inode_item_init+0x1d/0xa0 xfs_inode_item_init at fs/xfs/xfs_inode_item.c:639 [ 190.934461][ T369] xfs_trans_ijoin+0x96/0x100 xfs_trans_ijoin at fs/xfs/libxfs/xfs_trans_inode.c:34 [ 190.961530][ T369] xfs_setattr_nonsize+0x1a6/0xcd0 xfs_setattr_nonsize at fs/xfs/xfs_iops.c:716 [ 190.987331][ T369] xfs_vn_setattr+0x133/0x160 xfs_vn_setattr at fs/xfs/xfs_iops.c:1081 [ 191.010476][ T369] notify_change+0x6c5/0xba1 notify_change at fs/attr.c:336 [ 191.033317][ T369] chmod_common+0x19b/0x390 [ 191.055770][ T369] ksys_fchmod+0x28/0x60 [ 191.077957][ T369] __x64_sys_fchmod+0x4e/0x70 [ 191.102767][ T369] do_syscall_64+0x5f/0x310 [ 191.125090][ T369] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 191.153749][ T369] [ 191.153749][ T369] -> #0 (&xfs_nondir_ilock_class){++++}-{3:3}: [ 191.191267][ T369] __lock_acquire+0x2efc/0x4da0 [ 191.215974][ T369] lock_acquire+0x1ac/0xaf0 [ 191.238953][ T369] down_write_nested+0x92/0x150 [ 191.262955][ T369] xfs_reclaim_inode+0xdf/0x860 [ 191.287149][ T369] xfs_reclaim_inodes_ag+0x505/0xb00 [ 191.313291][ T369] xfs_reclaim_inodes_nr+0x93/0xd0 [ 191.338357][ T369] super_cache_scan+0x2fd/0x430 [ 191.362354][ T369] do_shrink_slab+0x317/0x990 [ 191.385341][ T369] shrink_slab+0x3a8/0x4b0 [ 191.407214][ T369] shrink_node+0x49c/0x17b0 [ 191.429841][ T369] balance_pgdat+0x59c/0xed0 [ 191.455041][ T369] kswapd+0x5a4/0xc40 [ 191.477524][ T369] kthread+0x358/0x420 [ 191.499285][ T369] ret_from_fork+0x22/0x30 [ 191.521107][ T369] [ 191.521107][ T369] other info that might help us debug this: [ 191.521107][ T369] [ 191.567490][ T369] Possible unsafe locking scenario: [ 191.567490][ T369] [ 191.600947][ T369] CPU0 CPU1 [ 191.624808][ T369] ---- ---- [ 191.649236][ T369] lock(fs_reclaim); [ 191.667607][ T369] lock(&xfs_nondir_ilock_class); [ 191.702096][ T369] lock(fs_reclaim); [ 191.731243][ T369] lock(&xfs_nondir_ilock_class); [ 191.754025][ T369] [ 191.754025][ T369] *** DEADLOCK *** [ 191.754025][ T369] [ 191.791126][ T369] 4 locks held by kswapd3/369: [ 191.812198][ T369] #0: ffffffffb50ced00 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x0/0x30 [ 191.854319][ T369] #1: ffffffffb5074c50 (shrinker_rwsem){++++}-{3:3}, at: shrink_slab+0x219/0x4b0 [ 191.896043][ T369] #2: ffff8890279b40e0 (&type->s_umount_key#27){++++}-{3:3}, at: trylock_super+0x11/0xb0 [ 191.940538][ T369] #3: ffff889027a73a28 (&pag->pag_ici_reclaim_lock){+.+.}-{3:3}, at: xfs_reclaim_inodes_ag+0x135/0xb00 [ 191.995314][ T369] [ 191.995314][ T369] stack backtrace: [ 192.022934][ T369] CPU: 42 PID: 369 Comm: kswapd3 Not tainted 5.8.0-rc1-next-20200621 #1 [ 192.060546][ T369] Hardware name: HP ProLiant BL660c Gen9, BIOS I38 10/17/2018 [ 192.094518][ T369] Call Trace: [ 192.109005][ T369] dump_stack+0x9d/0xe0 [ 192.127468][ T369] check_noncircular+0x347/0x400 [ 192.149526][ T369] ? print_circular_bug+0x360/0x360 [ 192.172584][ T369] ? freezing_slow_path.cold.2+0x2a/0x2a [ 192.197251][ T369] __lock_acquire+0x2efc/0x4da0 [ 192.218737][ T369] ? lockdep_hardirqs_on_prepare+0x550/0x550 [ 192.246736][ T369] ? __lock_acquire+0x3541/0x4da0 [ 192.269673][ T369] lock_acquire+0x1ac/0xaf0 [ 192.290192][ T369] ? xfs_reclaim_inode+0xdf/0x860 [ 192.313158][ T369] ? rcu_read_unlock+0x50/0x50 [ 192.335057][ T369] down_write_nested+0x92/0x150 [ 192.358409][ T369] ? xfs_reclaim_inode+0xdf/0x860 [ 192.380890][ T369] ? rwsem_down_write_slowpath+0xf50/0xf50 [ 192.406891][ T369] ? find_held_lock+0x33/0x1c0 [ 192.427925][ T369] ? xfs_ilock+0x2ef/0x370 [ 192.447496][ T369] ? xfs_reclaim_inode+0xdf/0x860 [ 192.472315][ T369] xfs_reclaim_inode+0xdf/0x860 [ 192.496649][ T369] ? xfs_inode_clear_reclaim_tag+0xa0/0xa0 [ 192.524188][ T369] ? do_raw_spin_unlock+0x4f/0x250 [ 192.546852][ T369] xfs_reclaim_inodes_ag+0x505/0xb00 [ 192.570473][ T369] ? xfs_reclaim_inode+0x860/0x860 [ 192.592692][ T369] ? mark_held_locks+0xb0/0x110 [ 192.614287][ T369] ? lockdep_hardirqs_on_prepare+0x38c/0x550 [ 192.640800][ T369] ? _raw_spin_unlock_irqrestore+0x39/0x40 [ 192.666695][ T369] ? try_to_wake_up+0xcf/0xf40 [ 192.688265][ T369] ? migrate_swap_stop+0xc10/0xc10 [ 192.711966][ T369] ? do_raw_spin_unlock+0x4f/0x250 [ 192.735032][ T369] xfs_reclaim_inodes_nr+0x93/0xd0 xfs_reclaim_inodes_nr at fs/xfs/xfs_icache.c:1399 [ 192.757674][ T369] ? xfs_reclaim_inodes+0x90/0x90 [ 192.780028][ T369] ? list_lru_count_one+0x177/0x300 [ 192.803010][ T369] super_cache_scan+0x2fd/0x430 super_cache_scan at fs/super.c:115 [ 192.824491][ T369] do_shrink_slab+0x317/0x990 do_shrink_slab at mm/vmscan.c:514 [ 192.845160][ T369] shrink_slab+0x3a8/0x4b0 shrink_slab_memcg at mm/vmscan.c:584 (inlined by) shrink_slab at mm/vmscan.c:662 [ 192.864722][ T369] ? do_shrink_slab+0x990/0x990 [ 192.886137][ T369] ? rcu_is_watching+0x2c/0x80 [ 192.907289][ T369] ? mem_cgroup_protected+0x228/0x470 [ 192.931166][ T369] ? vmpressure+0x25/0x290 [ 192.950595][ T369] shrink_node+0x49c/0x17b0 [ 192.972332][ T369] balance_pgdat+0x59c/0xed0 kswapd_shrink_node at mm/vmscan.c:3521 (inlined by) balance_pgdat at mm/vmscan.c:3670 [ 192.994918][ T369] ? __node_reclaim+0x950/0x950 [ 193.018625][ T369] ? lockdep_hardirqs_on_prepare+0x38c/0x550 [ 193.046566][ T369] ? _raw_spin_unlock_irq+0x1f/0x30 [ 193.070214][ T369] ? _raw_spin_unlock_irq+0x1f/0x30 [ 193.093176][ T369] ? finish_task_switch+0x129/0x650 [ 193.116225][ T369] ? finish_task_switch+0xf2/0x650 [ 193.138809][ T369] ? rcu_read_lock_bh_held+0xc0/0xc0 [ 193.163323][ T369] kswapd+0x5a4/0xc40 [ 193.182690][ T369] ? __kthread_parkme+0x4d/0x1a0 [ 193.204660][ T369] ? balance_pgdat+0xed0/0xed0 [ 193.225776][ T369] ? _raw_spin_unlock_irqrestore+0x39/0x40 [ 193.252306][ T369] ? finish_wait+0x270/0x270 [ 193.272473][ T369] ? __kthread_parkme+0x4d/0x1a0 [ 193.294476][ T369] ? __kthread_parkme+0xcc/0x1a0 [ 193.316704][ T369] ? balance_pgdat+0xed0/0xed0 [ 193.337808][ T369] kthread+0x358/0x420 [ 193.355666][ T369] ? kthread_create_worker_on_cpu+0xc0/0xc0 [ 193.381884][ T369] ret_from_fork+0x22/0x30 > --- > This is part of a gpu lockdep annotation series simply because it > really helps to catch issues where gpu subsystem locks and primitives > can deadlock with themselves through allocations and mmu notifiers. > But aside from that motivation it should be completely free-standing, > and can land through -mm/-rdma/-hmm or any other tree really whenever. > -Daniel > --- > mm/mmu_notifier.c | 7 ------- > mm/page_alloc.c | 25 ++++++++++++++++--------- > 2 files changed, 16 insertions(+), 16 deletions(-) > > diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c > index 06852b896fa6..5d578b9122f8 100644 > --- a/mm/mmu_notifier.c > +++ b/mm/mmu_notifier.c > @@ -612,13 +612,6 @@ int __mmu_notifier_register(struct mmu_notifier *subscription, > lockdep_assert_held_write(&mm->mmap_sem); > BUG_ON(atomic_read(&mm->mm_users) <= 0); > > - if (IS_ENABLED(CONFIG_LOCKDEP)) { > - fs_reclaim_acquire(GFP_KERNEL); > - lock_map_acquire(&__mmu_notifier_invalidate_range_start_map); > - lock_map_release(&__mmu_notifier_invalidate_range_start_map); > - fs_reclaim_release(GFP_KERNEL); > - } > - > if (!mm->notifier_subscriptions) { > /* > * kmalloc cannot be called under mm_take_all_locks(), but we > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 13cc653122b7..7536faaaa0fd 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -57,6 +57,7 @@ > #include <trace/events/oom.h> > #include <linux/prefetch.h> > #include <linux/mm_inline.h> > +#include <linux/mmu_notifier.h> > #include <linux/migrate.h> > #include <linux/hugetlb.h> > #include <linux/sched/rt.h> > @@ -4124,7 +4125,7 @@ should_compact_retry(struct alloc_context *ac, unsigned int order, int alloc_fla > static struct lockdep_map __fs_reclaim_map = > STATIC_LOCKDEP_MAP_INIT("fs_reclaim", &__fs_reclaim_map); > > -static bool __need_fs_reclaim(gfp_t gfp_mask) > +static bool __need_reclaim(gfp_t gfp_mask) > { > gfp_mask = current_gfp_context(gfp_mask); > > @@ -4136,10 +4137,6 @@ static bool __need_fs_reclaim(gfp_t gfp_mask) > if (current->flags & PF_MEMALLOC) > return false; > > - /* We're only interested __GFP_FS allocations for now */ > - if (!(gfp_mask & __GFP_FS)) > - return false; > - > if (gfp_mask & __GFP_NOLOCKDEP) > return false; > > @@ -4158,15 +4155,25 @@ void __fs_reclaim_release(void) > > void fs_reclaim_acquire(gfp_t gfp_mask) > { > - if (__need_fs_reclaim(gfp_mask)) > - __fs_reclaim_acquire(); > + if (__need_reclaim(gfp_mask)) { > + if (gfp_mask & __GFP_FS) > + __fs_reclaim_acquire(); > + > +#ifdef CONFIG_MMU_NOTIFIER > + lock_map_acquire(&__mmu_notifier_invalidate_range_start_map); > + lock_map_release(&__mmu_notifier_invalidate_range_start_map); > +#endif > + > + } > } > EXPORT_SYMBOL_GPL(fs_reclaim_acquire); > > void fs_reclaim_release(gfp_t gfp_mask) > { > - if (__need_fs_reclaim(gfp_mask)) > - __fs_reclaim_release(); > + if (__need_reclaim(gfp_mask)) { > + if (gfp_mask & __GFP_FS) > + __fs_reclaim_release(); > + } > } > EXPORT_SYMBOL_GPL(fs_reclaim_release); > #endif > -- > 2.26.2 > >
On Sun, Jun 21, 2020 at 7:42 PM Qian Cai <cai@lca.pw> wrote: > > On Wed, Jun 10, 2020 at 09:41:01PM +0200, Daniel Vetter wrote: > > fs_reclaim_acquire/release nicely catch recursion issues when > > allocating GFP_KERNEL memory against shrinkers (which gpu drivers tend > > to use to keep the excessive caches in check). For mmu notifier > > recursions we do have lockdep annotations since 23b68395c7c7 > > ("mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end"). > > > > But these only fire if a path actually results in some pte > > invalidation - for most small allocations that's very rarely the case. > > The other trouble is that pte invalidation can happen any time when > > __GFP_RECLAIM is set. Which means only really GFP_ATOMIC is a safe > > choice, GFP_NOIO isn't good enough to avoid potential mmu notifier > > recursion. > > > > I was pondering whether we should just do the general annotation, but > > there's always the risk for false positives. Plus I'm assuming that > > the core fs and io code is a lot better reviewed and tested than > > random mmu notifier code in drivers. Hence why I decide to only > > annotate for that specific case. > > > > Furthermore even if we'd create a lockdep map for direct reclaim, we'd > > still need to explicit pull in the mmu notifier map - there's a lot > > more places that do pte invalidation than just direct reclaim, these > > two contexts arent the same. > > > > Note that the mmu notifiers needing their own independent lockdep map > > is also the reason we can't hold them from fs_reclaim_acquire to > > fs_reclaim_release - it would nest with the acquistion in the pte > > invalidation code, causing a lockdep splat. And we can't remove the > > annotations from pte invalidation and all the other places since > > they're called from many other places than page reclaim. Hence we can > > only do the equivalent of might_lock, but on the raw lockdep map. > > > > With this we can also remove the lockdep priming added in 66204f1d2d1b > > ("mm/mmu_notifiers: prime lockdep") since the new annotations are > > strictly more powerful. > > > > v2: Review from Thomas Hellstrom: > > - unbotch the fs_reclaim context check, I accidentally inverted it, > > but it didn't blow up because I inverted it immediately > > - fix compiling for !CONFIG_MMU_NOTIFIER > > > > Cc: Thomas Hellström (Intel) <thomas_os@shipmail.org> > > Cc: Andrew Morton <akpm@linux-foundation.org> > > Cc: Jason Gunthorpe <jgg@mellanox.com> > > Cc: linux-mm@kvack.org > > Cc: linux-rdma@vger.kernel.org > > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> > > Cc: Christian König <christian.koenig@amd.com> > > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> > > Replying the right patch here... > > Reverting this commit [1] fixed the lockdep warning below while applying > some memory pressure. > > [1] linux-next cbf7c9d86d75 ("mm: track mmu notifiers in fs_reclaim_acquire/release") Hm, then I'm confused because - there's not mmut notifier lockdep map in the splat at a.. - the patch is supposed to not change anything for fs_reclaim (but the interim version got that wrong) - looking at the paths it's kmalloc vs kswapd, both places I totally expect fs_reflaim to be used. But you're claiming reverting this prevents the lockdep splat. If that's right, then my reasoning above is broken somewhere. Someone less blind than me having an idea? Aside this is the first email I've typed, until I realized the first report was against the broken patch and that looked like a much more reasonable explanation (but didn't quite match up with the code paths). Thanks, Daniel > > [ 190.455003][ T369] WARNING: possible circular locking dependency detected > [ 190.487291][ T369] 5.8.0-rc1-next-20200621 #1 Not tainted > [ 190.512363][ T369] ------------------------------------------------------ > [ 190.543354][ T369] kswapd3/369 is trying to acquire lock: > [ 190.568523][ T369] ffff889fcf694528 (&xfs_nondir_ilock_class){++++}-{3:3}, at: xfs_reclaim_inode+0xdf/0x860 > spin_lock at include/linux/spinlock.h:353 > (inlined by) xfs_iflags_test_and_set at fs/xfs/xfs_inode.h:166 > (inlined by) xfs_iflock_nowait at fs/xfs/xfs_inode.h:249 > (inlined by) xfs_reclaim_inode at fs/xfs/xfs_icache.c:1127 > [ 190.614359][ T369] > [ 190.614359][ T369] but task is already holding lock: > [ 190.647763][ T369] ffffffffb50ced00 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x0/0x30 > __fs_reclaim_acquire at mm/page_alloc.c:4200 > [ 190.687845][ T369] > [ 190.687845][ T369] which lock already depends on the new lock. > [ 190.687845][ T369] > [ 190.734890][ T369] > [ 190.734890][ T369] the existing dependency chain (in reverse order) is: > [ 190.775991][ T369] > [ 190.775991][ T369] -> #1 (fs_reclaim){+.+.}-{0:0}: > [ 190.808150][ T369] fs_reclaim_acquire+0x77/0x80 > [ 190.832152][ T369] slab_pre_alloc_hook.constprop.52+0x20/0x120 > slab_pre_alloc_hook at mm/slab.h:507 > [ 190.862173][ T369] kmem_cache_alloc+0x43/0x2a0 > [ 190.885602][ T369] kmem_zone_alloc+0x113/0x3ef > kmem_zone_alloc at fs/xfs/kmem.c:129 > [ 190.908702][ T369] xfs_inode_item_init+0x1d/0xa0 > xfs_inode_item_init at fs/xfs/xfs_inode_item.c:639 > [ 190.934461][ T369] xfs_trans_ijoin+0x96/0x100 > xfs_trans_ijoin at fs/xfs/libxfs/xfs_trans_inode.c:34 > [ 190.961530][ T369] xfs_setattr_nonsize+0x1a6/0xcd0 > xfs_setattr_nonsize at fs/xfs/xfs_iops.c:716 > [ 190.987331][ T369] xfs_vn_setattr+0x133/0x160 > xfs_vn_setattr at fs/xfs/xfs_iops.c:1081 > [ 191.010476][ T369] notify_change+0x6c5/0xba1 > notify_change at fs/attr.c:336 > [ 191.033317][ T369] chmod_common+0x19b/0x390 > [ 191.055770][ T369] ksys_fchmod+0x28/0x60 > [ 191.077957][ T369] __x64_sys_fchmod+0x4e/0x70 > [ 191.102767][ T369] do_syscall_64+0x5f/0x310 > [ 191.125090][ T369] entry_SYSCALL_64_after_hwframe+0x44/0xa9 > [ 191.153749][ T369] > [ 191.153749][ T369] -> #0 (&xfs_nondir_ilock_class){++++}-{3:3}: > [ 191.191267][ T369] __lock_acquire+0x2efc/0x4da0 > [ 191.215974][ T369] lock_acquire+0x1ac/0xaf0 > [ 191.238953][ T369] down_write_nested+0x92/0x150 > [ 191.262955][ T369] xfs_reclaim_inode+0xdf/0x860 > [ 191.287149][ T369] xfs_reclaim_inodes_ag+0x505/0xb00 > [ 191.313291][ T369] xfs_reclaim_inodes_nr+0x93/0xd0 > [ 191.338357][ T369] super_cache_scan+0x2fd/0x430 > [ 191.362354][ T369] do_shrink_slab+0x317/0x990 > [ 191.385341][ T369] shrink_slab+0x3a8/0x4b0 > [ 191.407214][ T369] shrink_node+0x49c/0x17b0 > [ 191.429841][ T369] balance_pgdat+0x59c/0xed0 > [ 191.455041][ T369] kswapd+0x5a4/0xc40 > [ 191.477524][ T369] kthread+0x358/0x420 > [ 191.499285][ T369] ret_from_fork+0x22/0x30 > [ 191.521107][ T369] > [ 191.521107][ T369] other info that might help us debug this: > [ 191.521107][ T369] > [ 191.567490][ T369] Possible unsafe locking scenario: > [ 191.567490][ T369] > [ 191.600947][ T369] CPU0 CPU1 > [ 191.624808][ T369] ---- ---- > [ 191.649236][ T369] lock(fs_reclaim); > [ 191.667607][ T369] lock(&xfs_nondir_ilock_class); > [ 191.702096][ T369] lock(fs_reclaim); > [ 191.731243][ T369] lock(&xfs_nondir_ilock_class); > [ 191.754025][ T369] > [ 191.754025][ T369] *** DEADLOCK *** > [ 191.754025][ T369] > [ 191.791126][ T369] 4 locks held by kswapd3/369: > [ 191.812198][ T369] #0: ffffffffb50ced00 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x0/0x30 > [ 191.854319][ T369] #1: ffffffffb5074c50 (shrinker_rwsem){++++}-{3:3}, at: shrink_slab+0x219/0x4b0 > [ 191.896043][ T369] #2: ffff8890279b40e0 (&type->s_umount_key#27){++++}-{3:3}, at: trylock_super+0x11/0xb0 > [ 191.940538][ T369] #3: ffff889027a73a28 (&pag->pag_ici_reclaim_lock){+.+.}-{3:3}, at: xfs_reclaim_inodes_ag+0x135/0xb00 > [ 191.995314][ T369] > [ 191.995314][ T369] stack backtrace: > [ 192.022934][ T369] CPU: 42 PID: 369 Comm: kswapd3 Not tainted 5.8.0-rc1-next-20200621 #1 > [ 192.060546][ T369] Hardware name: HP ProLiant BL660c Gen9, BIOS I38 10/17/2018 > [ 192.094518][ T369] Call Trace: > [ 192.109005][ T369] dump_stack+0x9d/0xe0 > [ 192.127468][ T369] check_noncircular+0x347/0x400 > [ 192.149526][ T369] ? print_circular_bug+0x360/0x360 > [ 192.172584][ T369] ? freezing_slow_path.cold.2+0x2a/0x2a > [ 192.197251][ T369] __lock_acquire+0x2efc/0x4da0 > [ 192.218737][ T369] ? lockdep_hardirqs_on_prepare+0x550/0x550 > [ 192.246736][ T369] ? __lock_acquire+0x3541/0x4da0 > [ 192.269673][ T369] lock_acquire+0x1ac/0xaf0 > [ 192.290192][ T369] ? xfs_reclaim_inode+0xdf/0x860 > [ 192.313158][ T369] ? rcu_read_unlock+0x50/0x50 > [ 192.335057][ T369] down_write_nested+0x92/0x150 > [ 192.358409][ T369] ? xfs_reclaim_inode+0xdf/0x860 > [ 192.380890][ T369] ? rwsem_down_write_slowpath+0xf50/0xf50 > [ 192.406891][ T369] ? find_held_lock+0x33/0x1c0 > [ 192.427925][ T369] ? xfs_ilock+0x2ef/0x370 > [ 192.447496][ T369] ? xfs_reclaim_inode+0xdf/0x860 > [ 192.472315][ T369] xfs_reclaim_inode+0xdf/0x860 > [ 192.496649][ T369] ? xfs_inode_clear_reclaim_tag+0xa0/0xa0 > [ 192.524188][ T369] ? do_raw_spin_unlock+0x4f/0x250 > [ 192.546852][ T369] xfs_reclaim_inodes_ag+0x505/0xb00 > [ 192.570473][ T369] ? xfs_reclaim_inode+0x860/0x860 > [ 192.592692][ T369] ? mark_held_locks+0xb0/0x110 > [ 192.614287][ T369] ? lockdep_hardirqs_on_prepare+0x38c/0x550 > [ 192.640800][ T369] ? _raw_spin_unlock_irqrestore+0x39/0x40 > [ 192.666695][ T369] ? try_to_wake_up+0xcf/0xf40 > [ 192.688265][ T369] ? migrate_swap_stop+0xc10/0xc10 > [ 192.711966][ T369] ? do_raw_spin_unlock+0x4f/0x250 > [ 192.735032][ T369] xfs_reclaim_inodes_nr+0x93/0xd0 > xfs_reclaim_inodes_nr at fs/xfs/xfs_icache.c:1399 > [ 192.757674][ T369] ? xfs_reclaim_inodes+0x90/0x90 > [ 192.780028][ T369] ? list_lru_count_one+0x177/0x300 > [ 192.803010][ T369] super_cache_scan+0x2fd/0x430 > super_cache_scan at fs/super.c:115 > [ 192.824491][ T369] do_shrink_slab+0x317/0x990 > do_shrink_slab at mm/vmscan.c:514 > [ 192.845160][ T369] shrink_slab+0x3a8/0x4b0 > shrink_slab_memcg at mm/vmscan.c:584 > (inlined by) shrink_slab at mm/vmscan.c:662 > [ 192.864722][ T369] ? do_shrink_slab+0x990/0x990 > [ 192.886137][ T369] ? rcu_is_watching+0x2c/0x80 > [ 192.907289][ T369] ? mem_cgroup_protected+0x228/0x470 > [ 192.931166][ T369] ? vmpressure+0x25/0x290 > [ 192.950595][ T369] shrink_node+0x49c/0x17b0 > [ 192.972332][ T369] balance_pgdat+0x59c/0xed0 > kswapd_shrink_node at mm/vmscan.c:3521 > (inlined by) balance_pgdat at mm/vmscan.c:3670 > [ 192.994918][ T369] ? __node_reclaim+0x950/0x950 > [ 193.018625][ T369] ? lockdep_hardirqs_on_prepare+0x38c/0x550 > [ 193.046566][ T369] ? _raw_spin_unlock_irq+0x1f/0x30 > [ 193.070214][ T369] ? _raw_spin_unlock_irq+0x1f/0x30 > [ 193.093176][ T369] ? finish_task_switch+0x129/0x650 > [ 193.116225][ T369] ? finish_task_switch+0xf2/0x650 > [ 193.138809][ T369] ? rcu_read_lock_bh_held+0xc0/0xc0 > [ 193.163323][ T369] kswapd+0x5a4/0xc40 > [ 193.182690][ T369] ? __kthread_parkme+0x4d/0x1a0 > [ 193.204660][ T369] ? balance_pgdat+0xed0/0xed0 > [ 193.225776][ T369] ? _raw_spin_unlock_irqrestore+0x39/0x40 > [ 193.252306][ T369] ? finish_wait+0x270/0x270 > [ 193.272473][ T369] ? __kthread_parkme+0x4d/0x1a0 > [ 193.294476][ T369] ? __kthread_parkme+0xcc/0x1a0 > [ 193.316704][ T369] ? balance_pgdat+0xed0/0xed0 > [ 193.337808][ T369] kthread+0x358/0x420 > [ 193.355666][ T369] ? kthread_create_worker_on_cpu+0xc0/0xc0 > [ 193.381884][ T369] ret_from_fork+0x22/0x30 > > > --- > > This is part of a gpu lockdep annotation series simply because it > > really helps to catch issues where gpu subsystem locks and primitives > > can deadlock with themselves through allocations and mmu notifiers. > > But aside from that motivation it should be completely free-standing, > > and can land through -mm/-rdma/-hmm or any other tree really whenever. > > -Daniel > > --- > > mm/mmu_notifier.c | 7 ------- > > mm/page_alloc.c | 25 ++++++++++++++++--------- > > 2 files changed, 16 insertions(+), 16 deletions(-) > > > > diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c > > index 06852b896fa6..5d578b9122f8 100644 > > --- a/mm/mmu_notifier.c > > +++ b/mm/mmu_notifier.c > > @@ -612,13 +612,6 @@ int __mmu_notifier_register(struct mmu_notifier *subscription, > > lockdep_assert_held_write(&mm->mmap_sem); > > BUG_ON(atomic_read(&mm->mm_users) <= 0); > > > > - if (IS_ENABLED(CONFIG_LOCKDEP)) { > > - fs_reclaim_acquire(GFP_KERNEL); > > - lock_map_acquire(&__mmu_notifier_invalidate_range_start_map); > > - lock_map_release(&__mmu_notifier_invalidate_range_start_map); > > - fs_reclaim_release(GFP_KERNEL); > > - } > > - > > if (!mm->notifier_subscriptions) { > > /* > > * kmalloc cannot be called under mm_take_all_locks(), but we > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 13cc653122b7..7536faaaa0fd 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -57,6 +57,7 @@ > > #include <trace/events/oom.h> > > #include <linux/prefetch.h> > > #include <linux/mm_inline.h> > > +#include <linux/mmu_notifier.h> > > #include <linux/migrate.h> > > #include <linux/hugetlb.h> > > #include <linux/sched/rt.h> > > @@ -4124,7 +4125,7 @@ should_compact_retry(struct alloc_context *ac, unsigned int order, int alloc_fla > > static struct lockdep_map __fs_reclaim_map = > > STATIC_LOCKDEP_MAP_INIT("fs_reclaim", &__fs_reclaim_map); > > > > -static bool __need_fs_reclaim(gfp_t gfp_mask) > > +static bool __need_reclaim(gfp_t gfp_mask) > > { > > gfp_mask = current_gfp_context(gfp_mask); > > > > @@ -4136,10 +4137,6 @@ static bool __need_fs_reclaim(gfp_t gfp_mask) > > if (current->flags & PF_MEMALLOC) > > return false; > > > > - /* We're only interested __GFP_FS allocations for now */ > > - if (!(gfp_mask & __GFP_FS)) > > - return false; > > - > > if (gfp_mask & __GFP_NOLOCKDEP) > > return false; > > > > @@ -4158,15 +4155,25 @@ void __fs_reclaim_release(void) > > > > void fs_reclaim_acquire(gfp_t gfp_mask) > > { > > - if (__need_fs_reclaim(gfp_mask)) > > - __fs_reclaim_acquire(); > > + if (__need_reclaim(gfp_mask)) { > > + if (gfp_mask & __GFP_FS) > > + __fs_reclaim_acquire(); > > + > > +#ifdef CONFIG_MMU_NOTIFIER > > + lock_map_acquire(&__mmu_notifier_invalidate_range_start_map); > > + lock_map_release(&__mmu_notifier_invalidate_range_start_map); > > +#endif > > + > > + } > > } > > EXPORT_SYMBOL_GPL(fs_reclaim_acquire); > > > > void fs_reclaim_release(gfp_t gfp_mask) > > { > > - if (__need_fs_reclaim(gfp_mask)) > > - __fs_reclaim_release(); > > + if (__need_reclaim(gfp_mask)) { > > + if (gfp_mask & __GFP_FS) > > + __fs_reclaim_release(); > > + } > > } > > EXPORT_SYMBOL_GPL(fs_reclaim_release); > > #endif > > -- > > 2.26.2 > > > >
On Sun, Jun 21, 2020 at 08:07:08PM +0200, Daniel Vetter wrote: > On Sun, Jun 21, 2020 at 7:42 PM Qian Cai <cai@lca.pw> wrote: > > > > On Wed, Jun 10, 2020 at 09:41:01PM +0200, Daniel Vetter wrote: > > > fs_reclaim_acquire/release nicely catch recursion issues when > > > allocating GFP_KERNEL memory against shrinkers (which gpu drivers tend > > > to use to keep the excessive caches in check). For mmu notifier > > > recursions we do have lockdep annotations since 23b68395c7c7 > > > ("mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end"). > > > > > > But these only fire if a path actually results in some pte > > > invalidation - for most small allocations that's very rarely the case. > > > The other trouble is that pte invalidation can happen any time when > > > __GFP_RECLAIM is set. Which means only really GFP_ATOMIC is a safe > > > choice, GFP_NOIO isn't good enough to avoid potential mmu notifier > > > recursion. > > > > > > I was pondering whether we should just do the general annotation, but > > > there's always the risk for false positives. Plus I'm assuming that > > > the core fs and io code is a lot better reviewed and tested than > > > random mmu notifier code in drivers. Hence why I decide to only > > > annotate for that specific case. > > > > > > Furthermore even if we'd create a lockdep map for direct reclaim, we'd > > > still need to explicit pull in the mmu notifier map - there's a lot > > > more places that do pte invalidation than just direct reclaim, these > > > two contexts arent the same. > > > > > > Note that the mmu notifiers needing their own independent lockdep map > > > is also the reason we can't hold them from fs_reclaim_acquire to > > > fs_reclaim_release - it would nest with the acquistion in the pte > > > invalidation code, causing a lockdep splat. And we can't remove the > > > annotations from pte invalidation and all the other places since > > > they're called from many other places than page reclaim. Hence we can > > > only do the equivalent of might_lock, but on the raw lockdep map. > > > > > > With this we can also remove the lockdep priming added in 66204f1d2d1b > > > ("mm/mmu_notifiers: prime lockdep") since the new annotations are > > > strictly more powerful. > > > > > > v2: Review from Thomas Hellstrom: > > > - unbotch the fs_reclaim context check, I accidentally inverted it, > > > but it didn't blow up because I inverted it immediately > > > - fix compiling for !CONFIG_MMU_NOTIFIER > > > > > > Cc: Thomas Hellström (Intel) <thomas_os@shipmail.org> > > > Cc: Andrew Morton <akpm@linux-foundation.org> > > > Cc: Jason Gunthorpe <jgg@mellanox.com> > > > Cc: linux-mm@kvack.org > > > Cc: linux-rdma@vger.kernel.org > > > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> > > > Cc: Christian König <christian.koenig@amd.com> > > > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> > > > > Replying the right patch here... > > > > Reverting this commit [1] fixed the lockdep warning below while applying > > some memory pressure. > > > > [1] linux-next cbf7c9d86d75 ("mm: track mmu notifiers in fs_reclaim_acquire/release") > > Hm, then I'm confused because > - there's not mmut notifier lockdep map in the splat at a.. > - the patch is supposed to not change anything for fs_reclaim (but the > interim version got that wrong) > - looking at the paths it's kmalloc vs kswapd, both places I totally > expect fs_reflaim to be used. > > But you're claiming reverting this prevents the lockdep splat. If > that's right, then my reasoning above is broken somewhere. Someone > less blind than me having an idea? > > Aside this is the first email I've typed, until I realized the first > report was against the broken patch and that looked like a much more > reasonable explanation (but didn't quite match up with the code > paths). Below diff should undo the functional change in my patch. Can you pls test whether the lockdep splat is really gone with that? Might need a lot of testing and memory pressure to be sure, since all these reclaim paths aren't very deterministic. -Daniel --- diff --git a/mm/page_alloc.c b/mm/page_alloc.c index d807587c9ae6..27ea763c6155 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -4191,11 +4191,6 @@ void fs_reclaim_acquire(gfp_t gfp_mask) if (gfp_mask & __GFP_FS) __fs_reclaim_acquire(); -#ifdef CONFIG_MMU_NOTIFIER - lock_map_acquire(&__mmu_notifier_invalidate_range_start_map); - lock_map_release(&__mmu_notifier_invalidate_range_start_map); -#endif - } } EXPORT_SYMBOL_GPL(fs_reclaim_acquire);
On Sun, Jun 21, 2020 at 10:01:03PM +0200, Daniel Vetter wrote: > On Sun, Jun 21, 2020 at 08:07:08PM +0200, Daniel Vetter wrote: > > On Sun, Jun 21, 2020 at 7:42 PM Qian Cai <cai@lca.pw> wrote: > > > > > > On Wed, Jun 10, 2020 at 09:41:01PM +0200, Daniel Vetter wrote: > > > > fs_reclaim_acquire/release nicely catch recursion issues when > > > > allocating GFP_KERNEL memory against shrinkers (which gpu drivers tend > > > > to use to keep the excessive caches in check). For mmu notifier > > > > recursions we do have lockdep annotations since 23b68395c7c7 > > > > ("mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end"). > > > > > > > > But these only fire if a path actually results in some pte > > > > invalidation - for most small allocations that's very rarely the case. > > > > The other trouble is that pte invalidation can happen any time when > > > > __GFP_RECLAIM is set. Which means only really GFP_ATOMIC is a safe > > > > choice, GFP_NOIO isn't good enough to avoid potential mmu notifier > > > > recursion. > > > > > > > > I was pondering whether we should just do the general annotation, but > > > > there's always the risk for false positives. Plus I'm assuming that > > > > the core fs and io code is a lot better reviewed and tested than > > > > random mmu notifier code in drivers. Hence why I decide to only > > > > annotate for that specific case. > > > > > > > > Furthermore even if we'd create a lockdep map for direct reclaim, we'd > > > > still need to explicit pull in the mmu notifier map - there's a lot > > > > more places that do pte invalidation than just direct reclaim, these > > > > two contexts arent the same. > > > > > > > > Note that the mmu notifiers needing their own independent lockdep map > > > > is also the reason we can't hold them from fs_reclaim_acquire to > > > > fs_reclaim_release - it would nest with the acquistion in the pte > > > > invalidation code, causing a lockdep splat. And we can't remove the > > > > annotations from pte invalidation and all the other places since > > > > they're called from many other places than page reclaim. Hence we can > > > > only do the equivalent of might_lock, but on the raw lockdep map. > > > > > > > > With this we can also remove the lockdep priming added in 66204f1d2d1b > > > > ("mm/mmu_notifiers: prime lockdep") since the new annotations are > > > > strictly more powerful. > > > > > > > > v2: Review from Thomas Hellstrom: > > > > - unbotch the fs_reclaim context check, I accidentally inverted it, > > > > but it didn't blow up because I inverted it immediately > > > > - fix compiling for !CONFIG_MMU_NOTIFIER > > > > > > > > Cc: Thomas Hellström (Intel) <thomas_os@shipmail.org> > > > > Cc: Andrew Morton <akpm@linux-foundation.org> > > > > Cc: Jason Gunthorpe <jgg@mellanox.com> > > > > Cc: linux-mm@kvack.org > > > > Cc: linux-rdma@vger.kernel.org > > > > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> > > > > Cc: Christian König <christian.koenig@amd.com> > > > > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> > > > > > > Replying the right patch here... > > > > > > Reverting this commit [1] fixed the lockdep warning below while applying > > > some memory pressure. > > > > > > [1] linux-next cbf7c9d86d75 ("mm: track mmu notifiers in fs_reclaim_acquire/release") > > > > Hm, then I'm confused because > > - there's not mmut notifier lockdep map in the splat at a.. > > - the patch is supposed to not change anything for fs_reclaim (but the > > interim version got that wrong) > > - looking at the paths it's kmalloc vs kswapd, both places I totally > > expect fs_reflaim to be used. > > > > But you're claiming reverting this prevents the lockdep splat. If > > that's right, then my reasoning above is broken somewhere. Someone > > less blind than me having an idea? > > > > Aside this is the first email I've typed, until I realized the first > > report was against the broken patch and that looked like a much more > > reasonable explanation (but didn't quite match up with the code > > paths). > > Below diff should undo the functional change in my patch. Can you pls test > whether the lockdep splat is really gone with that? Might need a lot of > testing and memory pressure to be sure, since all these reclaim paths > aren't very deterministic. Well, I am running even heavy memory pressure workloads on linux-next like every day, and never saw this splat until today where your patch first show up. Since I am rather busy tracking another regression, here is the steps to reproduce (super easy to reproduce on multiple machines here.): # git clone https://github.com/cailca/linux-mm.git # cd linux-mm; make # ./random 0 The .config is in there as well if ever matters.
On Sun, Jun 21, 2020 at 10:01:03PM +0200, Daniel Vetter wrote: > On Sun, Jun 21, 2020 at 08:07:08PM +0200, Daniel Vetter wrote: > > On Sun, Jun 21, 2020 at 7:42 PM Qian Cai <cai@lca.pw> wrote: > > > > > > On Wed, Jun 10, 2020 at 09:41:01PM +0200, Daniel Vetter wrote: > > > > fs_reclaim_acquire/release nicely catch recursion issues when > > > > allocating GFP_KERNEL memory against shrinkers (which gpu drivers tend > > > > to use to keep the excessive caches in check). For mmu notifier > > > > recursions we do have lockdep annotations since 23b68395c7c7 > > > > ("mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end"). > > > > > > > > But these only fire if a path actually results in some pte > > > > invalidation - for most small allocations that's very rarely the case. > > > > The other trouble is that pte invalidation can happen any time when > > > > __GFP_RECLAIM is set. Which means only really GFP_ATOMIC is a safe > > > > choice, GFP_NOIO isn't good enough to avoid potential mmu notifier > > > > recursion. > > > > > > > > I was pondering whether we should just do the general annotation, but > > > > there's always the risk for false positives. Plus I'm assuming that > > > > the core fs and io code is a lot better reviewed and tested than > > > > random mmu notifier code in drivers. Hence why I decide to only > > > > annotate for that specific case. > > > > > > > > Furthermore even if we'd create a lockdep map for direct reclaim, we'd > > > > still need to explicit pull in the mmu notifier map - there's a lot > > > > more places that do pte invalidation than just direct reclaim, these > > > > two contexts arent the same. > > > > > > > > Note that the mmu notifiers needing their own independent lockdep map > > > > is also the reason we can't hold them from fs_reclaim_acquire to > > > > fs_reclaim_release - it would nest with the acquistion in the pte > > > > invalidation code, causing a lockdep splat. And we can't remove the > > > > annotations from pte invalidation and all the other places since > > > > they're called from many other places than page reclaim. Hence we can > > > > only do the equivalent of might_lock, but on the raw lockdep map. > > > > > > > > With this we can also remove the lockdep priming added in 66204f1d2d1b > > > > ("mm/mmu_notifiers: prime lockdep") since the new annotations are > > > > strictly more powerful. > > > > > > > > v2: Review from Thomas Hellstrom: > > > > - unbotch the fs_reclaim context check, I accidentally inverted it, > > > > but it didn't blow up because I inverted it immediately > > > > - fix compiling for !CONFIG_MMU_NOTIFIER > > > > > > > > Cc: Thomas Hellström (Intel) <thomas_os@shipmail.org> > > > > Cc: Andrew Morton <akpm@linux-foundation.org> > > > > Cc: Jason Gunthorpe <jgg@mellanox.com> > > > > Cc: linux-mm@kvack.org > > > > Cc: linux-rdma@vger.kernel.org > > > > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> > > > > Cc: Christian König <christian.koenig@amd.com> > > > > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> > > > > > > Replying the right patch here... > > > > > > Reverting this commit [1] fixed the lockdep warning below while applying > > > some memory pressure. > > > > > > [1] linux-next cbf7c9d86d75 ("mm: track mmu notifiers in fs_reclaim_acquire/release") > > > > Hm, then I'm confused because > > - there's not mmut notifier lockdep map in the splat at a.. > > - the patch is supposed to not change anything for fs_reclaim (but the > > interim version got that wrong) > > - looking at the paths it's kmalloc vs kswapd, both places I totally > > expect fs_reflaim to be used. > > > > But you're claiming reverting this prevents the lockdep splat. If > > that's right, then my reasoning above is broken somewhere. Someone > > less blind than me having an idea? > > > > Aside this is the first email I've typed, until I realized the first > > report was against the broken patch and that looked like a much more > > reasonable explanation (but didn't quite match up with the code > > paths). > > Below diff should undo the functional change in my patch. Can you pls test > whether the lockdep splat is really gone with that? Might need a lot of > testing and memory pressure to be sure, since all these reclaim paths > aren't very deterministic. No, this patch does not help but reverting the whole patch still fixed the splat. > -Daniel > > --- > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index d807587c9ae6..27ea763c6155 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4191,11 +4191,6 @@ void fs_reclaim_acquire(gfp_t gfp_mask) > if (gfp_mask & __GFP_FS) > __fs_reclaim_acquire(); > > -#ifdef CONFIG_MMU_NOTIFIER > - lock_map_acquire(&__mmu_notifier_invalidate_range_start_map); > - lock_map_release(&__mmu_notifier_invalidate_range_start_map); > -#endif > - > } > } > EXPORT_SYMBOL_GPL(fs_reclaim_acquire); > -- > Daniel Vetter > Software Engineer, Intel Corporation > http://blog.ffwll.ch
On Tue, Jun 23, 2020 at 6:18 PM Qian Cai <cai@lca.pw> wrote: > > On Sun, Jun 21, 2020 at 10:01:03PM +0200, Daniel Vetter wrote: > > On Sun, Jun 21, 2020 at 08:07:08PM +0200, Daniel Vetter wrote: > > > On Sun, Jun 21, 2020 at 7:42 PM Qian Cai <cai@lca.pw> wrote: > > > > > > > > On Wed, Jun 10, 2020 at 09:41:01PM +0200, Daniel Vetter wrote: > > > > > fs_reclaim_acquire/release nicely catch recursion issues when > > > > > allocating GFP_KERNEL memory against shrinkers (which gpu drivers tend > > > > > to use to keep the excessive caches in check). For mmu notifier > > > > > recursions we do have lockdep annotations since 23b68395c7c7 > > > > > ("mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end"). > > > > > > > > > > But these only fire if a path actually results in some pte > > > > > invalidation - for most small allocations that's very rarely the case. > > > > > The other trouble is that pte invalidation can happen any time when > > > > > __GFP_RECLAIM is set. Which means only really GFP_ATOMIC is a safe > > > > > choice, GFP_NOIO isn't good enough to avoid potential mmu notifier > > > > > recursion. > > > > > > > > > > I was pondering whether we should just do the general annotation, but > > > > > there's always the risk for false positives. Plus I'm assuming that > > > > > the core fs and io code is a lot better reviewed and tested than > > > > > random mmu notifier code in drivers. Hence why I decide to only > > > > > annotate for that specific case. > > > > > > > > > > Furthermore even if we'd create a lockdep map for direct reclaim, we'd > > > > > still need to explicit pull in the mmu notifier map - there's a lot > > > > > more places that do pte invalidation than just direct reclaim, these > > > > > two contexts arent the same. > > > > > > > > > > Note that the mmu notifiers needing their own independent lockdep map > > > > > is also the reason we can't hold them from fs_reclaim_acquire to > > > > > fs_reclaim_release - it would nest with the acquistion in the pte > > > > > invalidation code, causing a lockdep splat. And we can't remove the > > > > > annotations from pte invalidation and all the other places since > > > > > they're called from many other places than page reclaim. Hence we can > > > > > only do the equivalent of might_lock, but on the raw lockdep map. > > > > > > > > > > With this we can also remove the lockdep priming added in 66204f1d2d1b > > > > > ("mm/mmu_notifiers: prime lockdep") since the new annotations are > > > > > strictly more powerful. > > > > > > > > > > v2: Review from Thomas Hellstrom: > > > > > - unbotch the fs_reclaim context check, I accidentally inverted it, > > > > > but it didn't blow up because I inverted it immediately > > > > > - fix compiling for !CONFIG_MMU_NOTIFIER > > > > > > > > > > Cc: Thomas Hellström (Intel) <thomas_os@shipmail.org> > > > > > Cc: Andrew Morton <akpm@linux-foundation.org> > > > > > Cc: Jason Gunthorpe <jgg@mellanox.com> > > > > > Cc: linux-mm@kvack.org > > > > > Cc: linux-rdma@vger.kernel.org > > > > > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> > > > > > Cc: Christian König <christian.koenig@amd.com> > > > > > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> > > > > > > > > Replying the right patch here... > > > > > > > > Reverting this commit [1] fixed the lockdep warning below while applying > > > > some memory pressure. > > > > > > > > [1] linux-next cbf7c9d86d75 ("mm: track mmu notifiers in fs_reclaim_acquire/release") > > > > > > Hm, then I'm confused because > > > - there's not mmut notifier lockdep map in the splat at a.. > > > - the patch is supposed to not change anything for fs_reclaim (but the > > > interim version got that wrong) > > > - looking at the paths it's kmalloc vs kswapd, both places I totally > > > expect fs_reflaim to be used. > > > > > > But you're claiming reverting this prevents the lockdep splat. If > > > that's right, then my reasoning above is broken somewhere. Someone > > > less blind than me having an idea? > > > > > > Aside this is the first email I've typed, until I realized the first > > > report was against the broken patch and that looked like a much more > > > reasonable explanation (but didn't quite match up with the code > > > paths). > > > > Below diff should undo the functional change in my patch. Can you pls test > > whether the lockdep splat is really gone with that? Might need a lot of > > testing and memory pressure to be sure, since all these reclaim paths > > aren't very deterministic. > > No, this patch does not help but reverting the whole patch still fixed > the splat. Ok I tested this. I can't use your script to repro because - I don't have a setup with xfs, and the splat points at an issue in xfs - reproducing lockdep splats in shrinker callbacks is always a bit tricky So instead I made a quick test to validate whether the fs_reclaim annotations work correctly, and nothing has changed: + printk("GFP_NOFS block\n"); + fs_reclaim_acquire(GFP_NOFS); + printk("allocate atomic\n"); + kfree(kmalloc(16, GFP_ATOMIC)); + printk("allocate noio\n"); + kfree(kmalloc(16, GFP_NOIO)); The below two calls to kmalloc are wrong, but the current annotations don't track __GFP_IO and other levels, only __GFP_FS. So no lockdep splats here. + printk("allocate nofs\n"); + kfree(kmalloc(16, GFP_NOFS)); + printk("allocate kernel\n"); + kfree(kmalloc(16, GFP_KERNEL)); + fs_reclaim_release(GFP_NOFS); + + + printk("GFP_KERNEL block\n"); + fs_reclaim_acquire(GFP_KERNEL); + printk("allocate atomic\n"); + kfree(kmalloc(16, GFP_ATOMIC)); + printk("allocate noio\n"); + kfree(kmalloc(16, GFP_NOIO)); + printk("allocate nofs\n"); + kfree(kmalloc(16, GFP_NOFS)); This allocation is buggy, and should splat. This is the case for both with my patch, and with my patch reverted. + printk("allocate kernel\n"); + kfree(kmalloc(16, GFP_KERNEL)); + fs_reclaim_release(GFP_KERNEL); I also looked at the paths in your lockdep splat in xfs, this is simply GFP_KERNEL vs a shrinker reclaim in kswapd. Summary: Everything is working as expected, there's no change in the lockdep annotations. I really think the problem is that either your testcase doesn't hit the issue reliably enough, or that you're not actually testing the same kernels and there's some other changes (xfs most likely, but really it could be anywhere) which is causing this regression. I'm rather convinced now after this test that it's not my stuff. Thanks, Daniel > > > -Daniel > > > > --- > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index d807587c9ae6..27ea763c6155 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -4191,11 +4191,6 @@ void fs_reclaim_acquire(gfp_t gfp_mask) > > if (gfp_mask & __GFP_FS) > > __fs_reclaim_acquire(); > > > > -#ifdef CONFIG_MMU_NOTIFIER > > - lock_map_acquire(&__mmu_notifier_invalidate_range_start_map); > > - lock_map_release(&__mmu_notifier_invalidate_range_start_map); > > -#endif > > - > > } > > } > > EXPORT_SYMBOL_GPL(fs_reclaim_acquire); > > -- > > Daniel Vetter > > Software Engineer, Intel Corporation > > http://blog.ffwll.ch
> On Jun 23, 2020, at 6:13 PM, Daniel Vetter <daniel@ffwll.ch> wrote: > > Ok I tested this. I can't use your script to repro because > - I don't have a setup with xfs, and the splat points at an issue in xfs > - reproducing lockdep splats in shrinker callbacks is always a bit tricky What’s xfs setup are you talking about? This is simple xfs rootfs and then trigger swapping. Nothing tricky here as it hit on multiple machines within a few seconds on linux-next. > Summary: Everything is working as expected, there's no change in the > lockdep annotations. > I really think the problem is that either your testcase doesn't hit > the issue reliably enough, or that you're not actually testing the > same kernels and there's some other changes (xfs most likely, but > really it could be anywhere) which is causing this regression. I'm > rather convinced now after this test that it's not my stuff. Well, the memory pressure workloads have been running for years on daily linux-next builds and never saw this one happened once. Also, the reverting is ONLY to revert your patch on the top of linux-next will stop the splat, so there is no not testing the same kernel at all.
On Sun, Jun 21, 2020 at 01:42:05PM -0400, Qian Cai wrote: > On Wed, Jun 10, 2020 at 09:41:01PM +0200, Daniel Vetter wrote: > > fs_reclaim_acquire/release nicely catch recursion issues when > > allocating GFP_KERNEL memory against shrinkers (which gpu drivers tend > > to use to keep the excessive caches in check). For mmu notifier > > recursions we do have lockdep annotations since 23b68395c7c7 > > ("mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end"). > > > > But these only fire if a path actually results in some pte > > invalidation - for most small allocations that's very rarely the case. > > The other trouble is that pte invalidation can happen any time when > > __GFP_RECLAIM is set. Which means only really GFP_ATOMIC is a safe > > choice, GFP_NOIO isn't good enough to avoid potential mmu notifier > > recursion. > > > > I was pondering whether we should just do the general annotation, but > > there's always the risk for false positives. Plus I'm assuming that > > the core fs and io code is a lot better reviewed and tested than > > random mmu notifier code in drivers. Hence why I decide to only > > annotate for that specific case. > > > > Furthermore even if we'd create a lockdep map for direct reclaim, we'd > > still need to explicit pull in the mmu notifier map - there's a lot > > more places that do pte invalidation than just direct reclaim, these > > two contexts arent the same. > > > > Note that the mmu notifiers needing their own independent lockdep map > > is also the reason we can't hold them from fs_reclaim_acquire to > > fs_reclaim_release - it would nest with the acquistion in the pte > > invalidation code, causing a lockdep splat. And we can't remove the > > annotations from pte invalidation and all the other places since > > they're called from many other places than page reclaim. Hence we can > > only do the equivalent of might_lock, but on the raw lockdep map. > > > > With this we can also remove the lockdep priming added in 66204f1d2d1b > > ("mm/mmu_notifiers: prime lockdep") since the new annotations are > > strictly more powerful. > > > > v2: Review from Thomas Hellstrom: > > - unbotch the fs_reclaim context check, I accidentally inverted it, > > but it didn't blow up because I inverted it immediately > > - fix compiling for !CONFIG_MMU_NOTIFIER > > > > Cc: Thomas Hellström (Intel) <thomas_os@shipmail.org> > > Cc: Andrew Morton <akpm@linux-foundation.org> > > Cc: Jason Gunthorpe <jgg@mellanox.com> > > Cc: linux-mm@kvack.org > > Cc: linux-rdma@vger.kernel.org > > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> > > Cc: Christian König <christian.koenig@amd.com> > > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> > > Replying the right patch here... > > Reverting this commit [1] fixed the lockdep warning below while applying > some memory pressure. > > [1] linux-next cbf7c9d86d75 ("mm: track mmu notifiers in fs_reclaim_acquire/release") > > [ 190.455003][ T369] WARNING: possible circular locking dependency detected > [ 190.487291][ T369] 5.8.0-rc1-next-20200621 #1 Not tainted > [ 190.512363][ T369] ------------------------------------------------------ > [ 190.543354][ T369] kswapd3/369 is trying to acquire lock: > [ 190.568523][ T369] ffff889fcf694528 (&xfs_nondir_ilock_class){++++}-{3:3}, at: xfs_reclaim_inode+0xdf/0x860 > spin_lock at include/linux/spinlock.h:353 > (inlined by) xfs_iflags_test_and_set at fs/xfs/xfs_inode.h:166 > (inlined by) xfs_iflock_nowait at fs/xfs/xfs_inode.h:249 > (inlined by) xfs_reclaim_inode at fs/xfs/xfs_icache.c:1127 > [ 190.614359][ T369] > [ 190.614359][ T369] but task is already holding lock: > [ 190.647763][ T369] ffffffffb50ced00 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x0/0x30 > __fs_reclaim_acquire at mm/page_alloc.c:4200 > [ 190.687845][ T369] > [ 190.687845][ T369] which lock already depends on the new lock. > [ 190.687845][ T369] > [ 190.734890][ T369] > [ 190.734890][ T369] the existing dependency chain (in reverse order) is: > [ 190.775991][ T369] > [ 190.775991][ T369] -> #1 (fs_reclaim){+.+.}-{0:0}: > [ 190.808150][ T369] fs_reclaim_acquire+0x77/0x80 > [ 190.832152][ T369] slab_pre_alloc_hook.constprop.52+0x20/0x120 > slab_pre_alloc_hook at mm/slab.h:507 > [ 190.862173][ T369] kmem_cache_alloc+0x43/0x2a0 > [ 190.885602][ T369] kmem_zone_alloc+0x113/0x3ef > kmem_zone_alloc at fs/xfs/kmem.c:129 > [ 190.908702][ T369] xfs_inode_item_init+0x1d/0xa0 > xfs_inode_item_init at fs/xfs/xfs_inode_item.c:639 > [ 190.934461][ T369] xfs_trans_ijoin+0x96/0x100 > xfs_trans_ijoin at fs/xfs/libxfs/xfs_trans_inode.c:34 > [ 190.961530][ T369] xfs_setattr_nonsize+0x1a6/0xcd0 OK, this patch has royally screwed something up if this path thinks it can enter memory reclaim. This path is inside a transaction, so it is running under PF_MEMALLOC_NOFS context, so should *never* enter memory reclaim. I'd suggest that whatever mods were made to fs_reclaim_acquire by this patch broke it's basic functionality.... > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 13cc653122b7..7536faaaa0fd 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -57,6 +57,7 @@ > > #include <trace/events/oom.h> > > #include <linux/prefetch.h> > > #include <linux/mm_inline.h> > > +#include <linux/mmu_notifier.h> > > #include <linux/migrate.h> > > #include <linux/hugetlb.h> > > #include <linux/sched/rt.h> > > @@ -4124,7 +4125,7 @@ should_compact_retry(struct alloc_context *ac, unsigned int order, int alloc_fla > > static struct lockdep_map __fs_reclaim_map = > > STATIC_LOCKDEP_MAP_INIT("fs_reclaim", &__fs_reclaim_map); > > > > -static bool __need_fs_reclaim(gfp_t gfp_mask) > > +static bool __need_reclaim(gfp_t gfp_mask) > > { > > gfp_mask = current_gfp_context(gfp_mask); This is applies the per-task memory allocation context flags to the mask that is checked here. > > @@ -4136,10 +4137,6 @@ static bool __need_fs_reclaim(gfp_t gfp_mask) > > if (current->flags & PF_MEMALLOC) > > return false; > > > > - /* We're only interested __GFP_FS allocations for now */ > > - if (!(gfp_mask & __GFP_FS)) > > - return false; > > - > > if (gfp_mask & __GFP_NOLOCKDEP) > > return false; > > > > @@ -4158,15 +4155,25 @@ void __fs_reclaim_release(void) > > > > void fs_reclaim_acquire(gfp_t gfp_mask) > > { > > - if (__need_fs_reclaim(gfp_mask)) > > - __fs_reclaim_acquire(); > > + if (__need_reclaim(gfp_mask)) { > > + if (gfp_mask & __GFP_FS) > > + __fs_reclaim_acquire(); .... and they have not been applied in this path. There's your breakage. For future reference, please post anything that changes NOFS allocation contexts or behaviours to linux-fsdevel, as filesystem developers need to know about proposed changes to infrastructure that is critical to the correct functioning of filesystems... Cheers, Dave.
On Wed, Jun 24, 2020 at 12:31 AM Dave Chinner <david@fromorbit.com> wrote: > > On Sun, Jun 21, 2020 at 01:42:05PM -0400, Qian Cai wrote: > > On Wed, Jun 10, 2020 at 09:41:01PM +0200, Daniel Vetter wrote: > > > fs_reclaim_acquire/release nicely catch recursion issues when > > > allocating GFP_KERNEL memory against shrinkers (which gpu drivers tend > > > to use to keep the excessive caches in check). For mmu notifier > > > recursions we do have lockdep annotations since 23b68395c7c7 > > > ("mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end"). > > > > > > But these only fire if a path actually results in some pte > > > invalidation - for most small allocations that's very rarely the case. > > > The other trouble is that pte invalidation can happen any time when > > > __GFP_RECLAIM is set. Which means only really GFP_ATOMIC is a safe > > > choice, GFP_NOIO isn't good enough to avoid potential mmu notifier > > > recursion. > > > > > > I was pondering whether we should just do the general annotation, but > > > there's always the risk for false positives. Plus I'm assuming that > > > the core fs and io code is a lot better reviewed and tested than > > > random mmu notifier code in drivers. Hence why I decide to only > > > annotate for that specific case. > > > > > > Furthermore even if we'd create a lockdep map for direct reclaim, we'd > > > still need to explicit pull in the mmu notifier map - there's a lot > > > more places that do pte invalidation than just direct reclaim, these > > > two contexts arent the same. > > > > > > Note that the mmu notifiers needing their own independent lockdep map > > > is also the reason we can't hold them from fs_reclaim_acquire to > > > fs_reclaim_release - it would nest with the acquistion in the pte > > > invalidation code, causing a lockdep splat. And we can't remove the > > > annotations from pte invalidation and all the other places since > > > they're called from many other places than page reclaim. Hence we can > > > only do the equivalent of might_lock, but on the raw lockdep map. > > > > > > With this we can also remove the lockdep priming added in 66204f1d2d1b > > > ("mm/mmu_notifiers: prime lockdep") since the new annotations are > > > strictly more powerful. > > > > > > v2: Review from Thomas Hellstrom: > > > - unbotch the fs_reclaim context check, I accidentally inverted it, > > > but it didn't blow up because I inverted it immediately > > > - fix compiling for !CONFIG_MMU_NOTIFIER > > > > > > Cc: Thomas Hellström (Intel) <thomas_os@shipmail.org> > > > Cc: Andrew Morton <akpm@linux-foundation.org> > > > Cc: Jason Gunthorpe <jgg@mellanox.com> > > > Cc: linux-mm@kvack.org > > > Cc: linux-rdma@vger.kernel.org > > > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> > > > Cc: Christian König <christian.koenig@amd.com> > > > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> > > > > Replying the right patch here... > > > > Reverting this commit [1] fixed the lockdep warning below while applying > > some memory pressure. > > > > [1] linux-next cbf7c9d86d75 ("mm: track mmu notifiers in fs_reclaim_acquire/release") > > > > [ 190.455003][ T369] WARNING: possible circular locking dependency detected > > [ 190.487291][ T369] 5.8.0-rc1-next-20200621 #1 Not tainted > > [ 190.512363][ T369] ------------------------------------------------------ > > [ 190.543354][ T369] kswapd3/369 is trying to acquire lock: > > [ 190.568523][ T369] ffff889fcf694528 (&xfs_nondir_ilock_class){++++}-{3:3}, at: xfs_reclaim_inode+0xdf/0x860 > > spin_lock at include/linux/spinlock.h:353 > > (inlined by) xfs_iflags_test_and_set at fs/xfs/xfs_inode.h:166 > > (inlined by) xfs_iflock_nowait at fs/xfs/xfs_inode.h:249 > > (inlined by) xfs_reclaim_inode at fs/xfs/xfs_icache.c:1127 > > [ 190.614359][ T369] > > [ 190.614359][ T369] but task is already holding lock: > > [ 190.647763][ T369] ffffffffb50ced00 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x0/0x30 > > __fs_reclaim_acquire at mm/page_alloc.c:4200 > > [ 190.687845][ T369] > > [ 190.687845][ T369] which lock already depends on the new lock. > > [ 190.687845][ T369] > > [ 190.734890][ T369] > > [ 190.734890][ T369] the existing dependency chain (in reverse order) is: > > [ 190.775991][ T369] > > [ 190.775991][ T369] -> #1 (fs_reclaim){+.+.}-{0:0}: > > [ 190.808150][ T369] fs_reclaim_acquire+0x77/0x80 > > [ 190.832152][ T369] slab_pre_alloc_hook.constprop.52+0x20/0x120 > > slab_pre_alloc_hook at mm/slab.h:507 > > [ 190.862173][ T369] kmem_cache_alloc+0x43/0x2a0 > > [ 190.885602][ T369] kmem_zone_alloc+0x113/0x3ef > > kmem_zone_alloc at fs/xfs/kmem.c:129 > > [ 190.908702][ T369] xfs_inode_item_init+0x1d/0xa0 > > xfs_inode_item_init at fs/xfs/xfs_inode_item.c:639 > > [ 190.934461][ T369] xfs_trans_ijoin+0x96/0x100 > > xfs_trans_ijoin at fs/xfs/libxfs/xfs_trans_inode.c:34 > > [ 190.961530][ T369] xfs_setattr_nonsize+0x1a6/0xcd0 > > OK, this patch has royally screwed something up if this path thinks > it can enter memory reclaim. This path is inside a transaction, so > it is running under PF_MEMALLOC_NOFS context, so should *never* > enter memory reclaim. > > I'd suggest that whatever mods were made to fs_reclaim_acquire by > this patch broke it's basic functionality.... > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > > index 13cc653122b7..7536faaaa0fd 100644 > > > --- a/mm/page_alloc.c > > > +++ b/mm/page_alloc.c > > > @@ -57,6 +57,7 @@ > > > #include <trace/events/oom.h> > > > #include <linux/prefetch.h> > > > #include <linux/mm_inline.h> > > > +#include <linux/mmu_notifier.h> > > > #include <linux/migrate.h> > > > #include <linux/hugetlb.h> > > > #include <linux/sched/rt.h> > > > @@ -4124,7 +4125,7 @@ should_compact_retry(struct alloc_context *ac, unsigned int order, int alloc_fla > > > static struct lockdep_map __fs_reclaim_map = > > > STATIC_LOCKDEP_MAP_INIT("fs_reclaim", &__fs_reclaim_map); > > > > > > -static bool __need_fs_reclaim(gfp_t gfp_mask) > > > +static bool __need_reclaim(gfp_t gfp_mask) > > > { > > > gfp_mask = current_gfp_context(gfp_mask); > > This is applies the per-task memory allocation context flags to the > mask that is checked here. > > > > @@ -4136,10 +4137,6 @@ static bool __need_fs_reclaim(gfp_t gfp_mask) > > > if (current->flags & PF_MEMALLOC) > > > return false; > > > > > > - /* We're only interested __GFP_FS allocations for now */ > > > - if (!(gfp_mask & __GFP_FS)) > > > - return false; > > > - > > > if (gfp_mask & __GFP_NOLOCKDEP) > > > return false; > > > > > > @@ -4158,15 +4155,25 @@ void __fs_reclaim_release(void) > > > > > > void fs_reclaim_acquire(gfp_t gfp_mask) > > > { > > > - if (__need_fs_reclaim(gfp_mask)) > > > - __fs_reclaim_acquire(); > > > + if (__need_reclaim(gfp_mask)) { > > > + if (gfp_mask & __GFP_FS) > > > + __fs_reclaim_acquire(); > > .... and they have not been applied in this path. There's your > breakage. > > For future reference, please post anything that changes NOFS > allocation contexts or behaviours to linux-fsdevel, as filesystem > developers need to know about proposed changes to infrastructure > that is critical to the correct functioning of filesystems... Uh crap I totally missed that. Apologies for wasting everyone's time here. Andrew, please drop for now, I respin this thing. -Daniel
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c index 06852b896fa6..5d578b9122f8 100644 --- a/mm/mmu_notifier.c +++ b/mm/mmu_notifier.c @@ -612,13 +612,6 @@ int __mmu_notifier_register(struct mmu_notifier *subscription, lockdep_assert_held_write(&mm->mmap_sem); BUG_ON(atomic_read(&mm->mm_users) <= 0); - if (IS_ENABLED(CONFIG_LOCKDEP)) { - fs_reclaim_acquire(GFP_KERNEL); - lock_map_acquire(&__mmu_notifier_invalidate_range_start_map); - lock_map_release(&__mmu_notifier_invalidate_range_start_map); - fs_reclaim_release(GFP_KERNEL); - } - if (!mm->notifier_subscriptions) { /* * kmalloc cannot be called under mm_take_all_locks(), but we diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 13cc653122b7..7536faaaa0fd 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -57,6 +57,7 @@ #include <trace/events/oom.h> #include <linux/prefetch.h> #include <linux/mm_inline.h> +#include <linux/mmu_notifier.h> #include <linux/migrate.h> #include <linux/hugetlb.h> #include <linux/sched/rt.h> @@ -4124,7 +4125,7 @@ should_compact_retry(struct alloc_context *ac, unsigned int order, int alloc_fla static struct lockdep_map __fs_reclaim_map = STATIC_LOCKDEP_MAP_INIT("fs_reclaim", &__fs_reclaim_map); -static bool __need_fs_reclaim(gfp_t gfp_mask) +static bool __need_reclaim(gfp_t gfp_mask) { gfp_mask = current_gfp_context(gfp_mask); @@ -4136,10 +4137,6 @@ static bool __need_fs_reclaim(gfp_t gfp_mask) if (current->flags & PF_MEMALLOC) return false; - /* We're only interested __GFP_FS allocations for now */ - if (!(gfp_mask & __GFP_FS)) - return false; - if (gfp_mask & __GFP_NOLOCKDEP) return false; @@ -4158,15 +4155,25 @@ void __fs_reclaim_release(void) void fs_reclaim_acquire(gfp_t gfp_mask) { - if (__need_fs_reclaim(gfp_mask)) - __fs_reclaim_acquire(); + if (__need_reclaim(gfp_mask)) { + if (gfp_mask & __GFP_FS) + __fs_reclaim_acquire(); + +#ifdef CONFIG_MMU_NOTIFIER + lock_map_acquire(&__mmu_notifier_invalidate_range_start_map); + lock_map_release(&__mmu_notifier_invalidate_range_start_map); +#endif + + } } EXPORT_SYMBOL_GPL(fs_reclaim_acquire); void fs_reclaim_release(gfp_t gfp_mask) { - if (__need_fs_reclaim(gfp_mask)) - __fs_reclaim_release(); + if (__need_reclaim(gfp_mask)) { + if (gfp_mask & __GFP_FS) + __fs_reclaim_release(); + } } EXPORT_SYMBOL_GPL(fs_reclaim_release); #endif
fs_reclaim_acquire/release nicely catch recursion issues when allocating GFP_KERNEL memory against shrinkers (which gpu drivers tend to use to keep the excessive caches in check). For mmu notifier recursions we do have lockdep annotations since 23b68395c7c7 ("mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end"). But these only fire if a path actually results in some pte invalidation - for most small allocations that's very rarely the case. The other trouble is that pte invalidation can happen any time when __GFP_RECLAIM is set. Which means only really GFP_ATOMIC is a safe choice, GFP_NOIO isn't good enough to avoid potential mmu notifier recursion. I was pondering whether we should just do the general annotation, but there's always the risk for false positives. Plus I'm assuming that the core fs and io code is a lot better reviewed and tested than random mmu notifier code in drivers. Hence why I decide to only annotate for that specific case. Furthermore even if we'd create a lockdep map for direct reclaim, we'd still need to explicit pull in the mmu notifier map - there's a lot more places that do pte invalidation than just direct reclaim, these two contexts arent the same. Note that the mmu notifiers needing their own independent lockdep map is also the reason we can't hold them from fs_reclaim_acquire to fs_reclaim_release - it would nest with the acquistion in the pte invalidation code, causing a lockdep splat. And we can't remove the annotations from pte invalidation and all the other places since they're called from many other places than page reclaim. Hence we can only do the equivalent of might_lock, but on the raw lockdep map. With this we can also remove the lockdep priming added in 66204f1d2d1b ("mm/mmu_notifiers: prime lockdep") since the new annotations are strictly more powerful. v2: Review from Thomas Hellstrom: - unbotch the fs_reclaim context check, I accidentally inverted it, but it didn't blow up because I inverted it immediately - fix compiling for !CONFIG_MMU_NOTIFIER Cc: Thomas Hellström (Intel) <thomas_os@shipmail.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: linux-mm@kvack.org Cc: linux-rdma@vger.kernel.org Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> Cc: Christian König <christian.koenig@amd.com> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> --- This is part of a gpu lockdep annotation series simply because it really helps to catch issues where gpu subsystem locks and primitives can deadlock with themselves through allocations and mmu notifiers. But aside from that motivation it should be completely free-standing, and can land through -mm/-rdma/-hmm or any other tree really whenever. -Daniel --- mm/mmu_notifier.c | 7 ------- mm/page_alloc.c | 25 ++++++++++++++++--------- 2 files changed, 16 insertions(+), 16 deletions(-)