| Message ID | 8cad21a9f0bcc2bd29a2b0e89e475687c44b3a59.1598996236.git.josef@toxicpanda.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Lockdep fixes | expand |
On 2/9/20 5:40 am, Josef Bacik wrote: > Nikolay reported a lockdep splat that I could reproduce with btrfs/187. > > ====================================================== > WARNING: possible circular locking dependency detected > 5.9.0-rc2+ #1 Tainted: G W > ------------------------------------------------------ > kswapd0/100 is trying to acquire lock: > ffff9e8ef38b6268 (&delayed_node->mutex){+.+.}-{3:3}, at: __btrfs_release_delayed_node.part.0+0x3f/0x330 > > but task is already holding lock: > ffffffffa9d74700 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x5/0x30 > > which lock already depends on the new lock. > > the existing dependency chain (in reverse order) is: > > -> #2 (fs_reclaim){+.+.}-{0:0}: > fs_reclaim_acquire+0x65/0x80 > slab_pre_alloc_hook.constprop.0+0x20/0x200 > kmem_cache_alloc_trace+0x3a/0x1a0 > btrfs_alloc_device+0x43/0x210 > add_missing_dev+0x20/0x90 > read_one_chunk+0x301/0x430 > btrfs_read_sys_array+0x17b/0x1b0 > open_ctree+0xa62/0x1896 > btrfs_mount_root.cold+0x12/0xea > legacy_get_tree+0x30/0x50 > vfs_get_tree+0x28/0xc0 > vfs_kern_mount.part.0+0x71/0xb0 > btrfs_mount+0x10d/0x379 > legacy_get_tree+0x30/0x50 > vfs_get_tree+0x28/0xc0 > path_mount+0x434/0xc00 > __x64_sys_mount+0xe3/0x120 > do_syscall_64+0x33/0x40 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > -> #1 (&fs_info->chunk_mutex){+.+.}-{3:3}: > __mutex_lock+0x7e/0x7e0 > btrfs_chunk_alloc+0x125/0x3a0 > find_free_extent+0xdf6/0x1210 > btrfs_reserve_extent+0xb3/0x1b0 > btrfs_alloc_tree_block+0xb0/0x310 > alloc_tree_block_no_bg_flush+0x4a/0x60 > __btrfs_cow_block+0x11a/0x530 > btrfs_cow_block+0x104/0x220 > btrfs_search_slot+0x52e/0x9d0 > btrfs_lookup_inode+0x2a/0x8f > __btrfs_update_delayed_inode+0x80/0x240 > btrfs_commit_inode_delayed_inode+0x119/0x120 > btrfs_evict_inode+0x357/0x500 > evict+0xcf/0x1f0 > vfs_rmdir.part.0+0x149/0x160 > do_rmdir+0x136/0x1a0 > do_syscall_64+0x33/0x40 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > -> #0 (&delayed_node->mutex){+.+.}-{3:3}: > __lock_acquire+0x1184/0x1fa0 > lock_acquire+0xa4/0x3d0 > __mutex_lock+0x7e/0x7e0 > __btrfs_release_delayed_node.part.0+0x3f/0x330 > btrfs_evict_inode+0x24c/0x500 > evict+0xcf/0x1f0 > dispose_list+0x48/0x70 > prune_icache_sb+0x44/0x50 > super_cache_scan+0x161/0x1e0 > do_shrink_slab+0x178/0x3c0 > shrink_slab+0x17c/0x290 > shrink_node+0x2b2/0x6d0 > balance_pgdat+0x30a/0x670 > kswapd+0x213/0x4c0 > kthread+0x138/0x160 > ret_from_fork+0x1f/0x30 > > other info that might help us debug this: > > Chain exists of: > &delayed_node->mutex --> &fs_info->chunk_mutex --> fs_reclaim > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(fs_reclaim); > lock(&fs_info->chunk_mutex); > lock(fs_reclaim); > lock(&delayed_node->mutex); > > *** DEADLOCK *** > > 3 locks held by kswapd0/100: > #0: ffffffffa9d74700 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x5/0x30 > #1: ffffffffa9d65c50 (shrinker_rwsem){++++}-{3:3}, at: shrink_slab+0x115/0x290 > #2: ffff9e8e9da260e0 (&type->s_umount_key#48){++++}-{3:3}, at: super_cache_scan+0x38/0x1e0 > > stack backtrace: > CPU: 1 PID: 100 Comm: kswapd0 Tainted: G W 5.9.0-rc2+ #1 > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014 > Call Trace: > dump_stack+0x92/0xc8 > check_noncircular+0x12d/0x150 > __lock_acquire+0x1184/0x1fa0 > lock_acquire+0xa4/0x3d0 > ? __btrfs_release_delayed_node.part.0+0x3f/0x330 > __mutex_lock+0x7e/0x7e0 > ? __btrfs_release_delayed_node.part.0+0x3f/0x330 > ? __btrfs_release_delayed_node.part.0+0x3f/0x330 > ? lock_acquire+0xa4/0x3d0 > ? btrfs_evict_inode+0x11e/0x500 > ? find_held_lock+0x2b/0x80 > __btrfs_release_delayed_node.part.0+0x3f/0x330 > btrfs_evict_inode+0x24c/0x500 > evict+0xcf/0x1f0 > dispose_list+0x48/0x70 > prune_icache_sb+0x44/0x50 > super_cache_scan+0x161/0x1e0 > do_shrink_slab+0x178/0x3c0 > shrink_slab+0x17c/0x290 > shrink_node+0x2b2/0x6d0 > balance_pgdat+0x30a/0x670 > kswapd+0x213/0x4c0 > ? _raw_spin_unlock_irqrestore+0x46/0x60 > ? add_wait_queue_exclusive+0x70/0x70 > ? balance_pgdat+0x670/0x670 > kthread+0x138/0x160 > ? kthread_create_worker_on_cpu+0x40/0x40 > ret_from_fork+0x1f/0x30 > > This is because we are holding the chunk_mutex when we call > btrfs_alloc_device, which does a GFP_KERNEL allocation. We don't want > to switch that to a GFP_NOFS lock because this is the only place where > it matters. So instead use memalloc_nofs_save() around the allocation > in order to avoid the lockdep splat. > > References: https://github.com/btrfs/fstests/issues/6 > Signed-off-by: Josef Bacik <josef@toxicpanda.com> > --- > fs/btrfs/volumes.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c > index 3f8bd1af29eb..d6bbbe1986bb 100644 > --- a/fs/btrfs/volumes.c > +++ b/fs/btrfs/volumes.c > @@ -4,6 +4,7 @@ > */ > > #include <linux/sched.h> > +#include <linux/sched/mm.h> > #include <linux/bio.h> > #include <linux/slab.h> > #include <linux/blkdev.h> > @@ -6480,8 +6481,17 @@ static struct btrfs_device *add_missing_dev(struct btrfs_fs_devices *fs_devices, > u64 devid, u8 *dev_uuid) > { > struct btrfs_device *device; > + unsigned int nofs_flag; > > + /* > + * We call this under the chunk_mutex, so we want to use NOFS for this > + * allocation, however we don't want to change btrfs_alloc_device() to > + * always do NOFS because we use it in a lot of other GFP_KERNEL safe > + * places. > + */ > + nofs_flag = memalloc_nofs_save(); > device = btrfs_alloc_device(NULL, &devid, dev_uuid); > + memalloc_nofs_restore(nofs_flag); > if (IS_ERR(device)) > return device; > > looks good. Reviewed-by: Anand Jain <anand.jain@oracle.com> Thanks, Anand
On Tue, Sep 01, 2020 at 05:40:35PM -0400, Josef Bacik wrote: > > References: https://github.com/btrfs/fstests/issues/6 > Signed-off-by: Josef Bacik <josef@toxicpanda.com> Added to misc-next, thanks.
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 3f8bd1af29eb..d6bbbe1986bb 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -4,6 +4,7 @@ */ #include <linux/sched.h> +#include <linux/sched/mm.h> #include <linux/bio.h> #include <linux/slab.h> #include <linux/blkdev.h> @@ -6480,8 +6481,17 @@ static struct btrfs_device *add_missing_dev(struct btrfs_fs_devices *fs_devices, u64 devid, u8 *dev_uuid) { struct btrfs_device *device; + unsigned int nofs_flag; + /* + * We call this under the chunk_mutex, so we want to use NOFS for this + * allocation, however we don't want to change btrfs_alloc_device() to + * always do NOFS because we use it in a lot of other GFP_KERNEL safe + * places. + */ + nofs_flag = memalloc_nofs_save(); device = btrfs_alloc_device(NULL, &devid, dev_uuid); + memalloc_nofs_restore(nofs_flag); if (IS_ERR(device)) return device;
Nikolay reported a lockdep splat that I could reproduce with btrfs/187. ====================================================== WARNING: possible circular locking dependency detected 5.9.0-rc2+ #1 Tainted: G W ------------------------------------------------------ kswapd0/100 is trying to acquire lock: ffff9e8ef38b6268 (&delayed_node->mutex){+.+.}-{3:3}, at: __btrfs_release_delayed_node.part.0+0x3f/0x330 but task is already holding lock: ffffffffa9d74700 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x5/0x30 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (fs_reclaim){+.+.}-{0:0}: fs_reclaim_acquire+0x65/0x80 slab_pre_alloc_hook.constprop.0+0x20/0x200 kmem_cache_alloc_trace+0x3a/0x1a0 btrfs_alloc_device+0x43/0x210 add_missing_dev+0x20/0x90 read_one_chunk+0x301/0x430 btrfs_read_sys_array+0x17b/0x1b0 open_ctree+0xa62/0x1896 btrfs_mount_root.cold+0x12/0xea legacy_get_tree+0x30/0x50 vfs_get_tree+0x28/0xc0 vfs_kern_mount.part.0+0x71/0xb0 btrfs_mount+0x10d/0x379 legacy_get_tree+0x30/0x50 vfs_get_tree+0x28/0xc0 path_mount+0x434/0xc00 __x64_sys_mount+0xe3/0x120 do_syscall_64+0x33/0x40 entry_SYSCALL_64_after_hwframe+0x44/0xa9 -> #1 (&fs_info->chunk_mutex){+.+.}-{3:3}: __mutex_lock+0x7e/0x7e0 btrfs_chunk_alloc+0x125/0x3a0 find_free_extent+0xdf6/0x1210 btrfs_reserve_extent+0xb3/0x1b0 btrfs_alloc_tree_block+0xb0/0x310 alloc_tree_block_no_bg_flush+0x4a/0x60 __btrfs_cow_block+0x11a/0x530 btrfs_cow_block+0x104/0x220 btrfs_search_slot+0x52e/0x9d0 btrfs_lookup_inode+0x2a/0x8f __btrfs_update_delayed_inode+0x80/0x240 btrfs_commit_inode_delayed_inode+0x119/0x120 btrfs_evict_inode+0x357/0x500 evict+0xcf/0x1f0 vfs_rmdir.part.0+0x149/0x160 do_rmdir+0x136/0x1a0 do_syscall_64+0x33/0x40 entry_SYSCALL_64_after_hwframe+0x44/0xa9 -> #0 (&delayed_node->mutex){+.+.}-{3:3}: __lock_acquire+0x1184/0x1fa0 lock_acquire+0xa4/0x3d0 __mutex_lock+0x7e/0x7e0 __btrfs_release_delayed_node.part.0+0x3f/0x330 btrfs_evict_inode+0x24c/0x500 evict+0xcf/0x1f0 dispose_list+0x48/0x70 prune_icache_sb+0x44/0x50 super_cache_scan+0x161/0x1e0 do_shrink_slab+0x178/0x3c0 shrink_slab+0x17c/0x290 shrink_node+0x2b2/0x6d0 balance_pgdat+0x30a/0x670 kswapd+0x213/0x4c0 kthread+0x138/0x160 ret_from_fork+0x1f/0x30 other info that might help us debug this: Chain exists of: &delayed_node->mutex --> &fs_info->chunk_mutex --> fs_reclaim Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(fs_reclaim); lock(&fs_info->chunk_mutex); lock(fs_reclaim); lock(&delayed_node->mutex); *** DEADLOCK *** 3 locks held by kswapd0/100: #0: ffffffffa9d74700 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x5/0x30 #1: ffffffffa9d65c50 (shrinker_rwsem){++++}-{3:3}, at: shrink_slab+0x115/0x290 #2: ffff9e8e9da260e0 (&type->s_umount_key#48){++++}-{3:3}, at: super_cache_scan+0x38/0x1e0 stack backtrace: CPU: 1 PID: 100 Comm: kswapd0 Tainted: G W 5.9.0-rc2+ #1 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014 Call Trace: dump_stack+0x92/0xc8 check_noncircular+0x12d/0x150 __lock_acquire+0x1184/0x1fa0 lock_acquire+0xa4/0x3d0 ? __btrfs_release_delayed_node.part.0+0x3f/0x330 __mutex_lock+0x7e/0x7e0 ? __btrfs_release_delayed_node.part.0+0x3f/0x330 ? __btrfs_release_delayed_node.part.0+0x3f/0x330 ? lock_acquire+0xa4/0x3d0 ? btrfs_evict_inode+0x11e/0x500 ? find_held_lock+0x2b/0x80 __btrfs_release_delayed_node.part.0+0x3f/0x330 btrfs_evict_inode+0x24c/0x500 evict+0xcf/0x1f0 dispose_list+0x48/0x70 prune_icache_sb+0x44/0x50 super_cache_scan+0x161/0x1e0 do_shrink_slab+0x178/0x3c0 shrink_slab+0x17c/0x290 shrink_node+0x2b2/0x6d0 balance_pgdat+0x30a/0x670 kswapd+0x213/0x4c0 ? _raw_spin_unlock_irqrestore+0x46/0x60 ? add_wait_queue_exclusive+0x70/0x70 ? balance_pgdat+0x670/0x670 kthread+0x138/0x160 ? kthread_create_worker_on_cpu+0x40/0x40 ret_from_fork+0x1f/0x30 This is because we are holding the chunk_mutex when we call btrfs_alloc_device, which does a GFP_KERNEL allocation. We don't want to switch that to a GFP_NOFS lock because this is the only place where it matters. So instead use memalloc_nofs_save() around the allocation in order to avoid the lockdep splat. References: https://github.com/btrfs/fstests/issues/6 Signed-off-by: Josef Bacik <josef@toxicpanda.com> --- fs/btrfs/volumes.c | 10 ++++++++++ 1 file changed, 10 insertions(+)