diff mbox

[1/6] lockdep: allow to disable reclaim lockup detection

Message ID 20170206140718.16222-2-mhocko@kernel.org (mailing list archive)
State Superseded, archived
Headers show

Commit Message

Michal Hocko Feb. 6, 2017, 2:07 p.m. UTC 
From: Michal Hocko <mhocko@suse.com>

The current implementation of the reclaim lockup detection can lead to
false positives and those even happen and usually lead to tweak the
code to silence the lockdep by using GFP_NOFS even though the context
can use __GFP_FS just fine. See
http://lkml.kernel.org/r/20160512080321.GA18496@dastard as an example.

Comments

Matthew Wilcox Feb. 6, 2017, 2:26 p.m. UTC | #1 
On Mon, Feb 06, 2017 at 03:07:13PM +0100, Michal Hocko wrote:
> While we are at it also make sure that the radix tree doesn't
> accidentaly override tags stored in the upper part of the gfp_mask.

> diff --git a/lib/radix-tree.c b/lib/radix-tree.c
> index 9dc093d5ef39..7550be09f9d6 100644
> --- a/lib/radix-tree.c
> +++ b/lib/radix-tree.c
> @@ -2274,6 +2274,8 @@ static int radix_tree_cpu_dead(unsigned int cpu)
>  void __init radix_tree_init(void)
>  {
>  	int ret;
> +
> +	BUILD_BUG_ON(RADIX_TREE_MAX_TAGS + __GFP_BITS_SHIFT > 32);
>  	radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
>  			sizeof(struct radix_tree_node), 0,
>  			SLAB_PANIC | SLAB_RECLAIM_ACCOUNT,

That's going to have a conceptual conflict with some patches I have
in flight.  I'll take this part through my radix tree patch collection.
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Michal Hocko Feb. 6, 2017, 2:34 p.m. UTC | #2 
On Mon 06-02-17 06:26:41, Matthew Wilcox wrote:
> On Mon, Feb 06, 2017 at 03:07:13PM +0100, Michal Hocko wrote:
> > While we are at it also make sure that the radix tree doesn't
> > accidentaly override tags stored in the upper part of the gfp_mask.
> 
> > diff --git a/lib/radix-tree.c b/lib/radix-tree.c
> > index 9dc093d5ef39..7550be09f9d6 100644
> > --- a/lib/radix-tree.c
> > +++ b/lib/radix-tree.c
> > @@ -2274,6 +2274,8 @@ static int radix_tree_cpu_dead(unsigned int cpu)
> >  void __init radix_tree_init(void)
> >  {
> >  	int ret;
> > +
> > +	BUILD_BUG_ON(RADIX_TREE_MAX_TAGS + __GFP_BITS_SHIFT > 32);
> >  	radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
> >  			sizeof(struct radix_tree_node), 0,
> >  			SLAB_PANIC | SLAB_RECLAIM_ACCOUNT,
> 
> That's going to have a conceptual conflict with some patches I have
> in flight.  I'll take this part through my radix tree patch collection.

This part is not needed for the patch, strictly speaking but I wanted to
make the code more future proof.
Matthew Wilcox Feb. 6, 2017, 3:24 p.m. UTC | #3 
On Mon, Feb 06, 2017 at 03:34:50PM +0100, Michal Hocko wrote:
> This part is not needed for the patch, strictly speaking but I wanted to
> make the code more future proof.

Understood.  I took an extra bit myself for marking the radix tree as
being used for an IDR (so the radix tree now uses 4 bits).  I see you
already split out the address space GFP mask from the other flags :-)
I would prefer not to do that with the radix tree, but I understand
your desire for more GFP bits.  I'm not entirely sure that an implicit
gfpmask makes a lot of sense for the radix tree, but it'd be a big effort
to change all the callers.  Anyway, I'm going to update your line here
for my current tree and add the build bug so we'll know if we ever hit
any problems.
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Michal Hocko Feb. 6, 2017, 3:30 p.m. UTC | #4 
On Mon 06-02-17 07:24:00, Matthew Wilcox wrote:
> On Mon, Feb 06, 2017 at 03:34:50PM +0100, Michal Hocko wrote:
> > This part is not needed for the patch, strictly speaking but I wanted to
> > make the code more future proof.
> 
> Understood.  I took an extra bit myself for marking the radix tree as
> being used for an IDR (so the radix tree now uses 4 bits).  I see you
> already split out the address space GFP mask from the other flags :-)
> I would prefer not to do that with the radix tree, but I understand
> your desire for more GFP bits.  I'm not entirely sure that an implicit
> gfpmask makes a lot of sense for the radix tree, but it'd be a big effort
> to change all the callers.  Anyway, I'm going to update your line here
> for my current tree and add the build bug so we'll know if we ever hit
> any problems.

OK, do I get it right that the patch can stay as is and go to Andrew?
I would really like to not rebase the patch again for something that is
not merged yet. I really hope for getting this merged finally...
diff mbox

Patch

=================================
[ INFO: inconsistent lock state ]
4.5.0-rc2+ #4 Tainted: G           O
---------------------------------
inconsistent {RECLAIM_FS-ON-R} -> {IN-RECLAIM_FS-W} usage.
kswapd0/543 [HC0[0]:SC0[0]:HE1:SE1] takes:

(&xfs_nondir_ilock_class){++++-+}, at: [<ffffffffa00781f7>] xfs_ilock+0x177/0x200 [xfs]

{RECLAIM_FS-ON-R} state was registered at:
  [<ffffffff8110f369>] mark_held_locks+0x79/0xa0
  [<ffffffff81113a43>] lockdep_trace_alloc+0xb3/0x100
  [<ffffffff81224623>] kmem_cache_alloc+0x33/0x230
  [<ffffffffa008acc1>] kmem_zone_alloc+0x81/0x120 [xfs]
  [<ffffffffa005456e>] xfs_refcountbt_init_cursor+0x3e/0xa0 [xfs]
  [<ffffffffa0053455>] __xfs_refcount_find_shared+0x75/0x580 [xfs]
  [<ffffffffa00539e4>] xfs_refcount_find_shared+0x84/0xb0 [xfs]
  [<ffffffffa005dcb8>] xfs_getbmap+0x608/0x8c0 [xfs]
  [<ffffffffa007634b>] xfs_vn_fiemap+0xab/0xc0 [xfs]
  [<ffffffff81244208>] do_vfs_ioctl+0x498/0x670
  [<ffffffff81244459>] SyS_ioctl+0x79/0x90
  [<ffffffff81847cd7>] entry_SYSCALL_64_fastpath+0x12/0x6f

       CPU0
       ----
  lock(&xfs_nondir_ilock_class);
  <Interrupt>
    lock(&xfs_nondir_ilock_class);

 *** DEADLOCK ***

3 locks held by kswapd0/543:

stack backtrace:
CPU: 0 PID: 543 Comm: kswapd0 Tainted: G           O    4.5.0-rc2+ #4

Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006

 ffffffff82a34f10 ffff88003aa078d0 ffffffff813a14f9 ffff88003d8551c0
 ffff88003aa07920 ffffffff8110ec65 0000000000000000 0000000000000001
 ffff880000000001 000000000000000b 0000000000000008 ffff88003d855aa0
Call Trace:
 [<ffffffff813a14f9>] dump_stack+0x4b/0x72
 [<ffffffff8110ec65>] print_usage_bug+0x215/0x240
 [<ffffffff8110ee85>] mark_lock+0x1f5/0x660
 [<ffffffff8110e100>] ? print_shortest_lock_dependencies+0x1a0/0x1a0
 [<ffffffff811102e0>] __lock_acquire+0xa80/0x1e50
 [<ffffffff8122474e>] ? kmem_cache_alloc+0x15e/0x230
 [<ffffffffa008acc1>] ? kmem_zone_alloc+0x81/0x120 [xfs]
 [<ffffffff811122e8>] lock_acquire+0xd8/0x1e0
 [<ffffffffa00781f7>] ? xfs_ilock+0x177/0x200 [xfs]
 [<ffffffffa0083a70>] ? xfs_reflink_cancel_cow_range+0x150/0x300 [xfs]
 [<ffffffff8110aace>] down_write_nested+0x5e/0xc0
 [<ffffffffa00781f7>] ? xfs_ilock+0x177/0x200 [xfs]
 [<ffffffffa00781f7>] xfs_ilock+0x177/0x200 [xfs]
 [<ffffffffa0083a70>] xfs_reflink_cancel_cow_range+0x150/0x300 [xfs]
 [<ffffffffa0085bdc>] xfs_fs_evict_inode+0xdc/0x1e0 [xfs]
 [<ffffffff8124d7d5>] evict+0xc5/0x190
 [<ffffffff8124d8d9>] dispose_list+0x39/0x60
 [<ffffffff8124eb2b>] prune_icache_sb+0x4b/0x60
 [<ffffffff8123317f>] super_cache_scan+0x14f/0x1a0
 [<ffffffff811e0d19>] shrink_slab.part.63.constprop.79+0x1e9/0x4e0
 [<ffffffff811e50ee>] shrink_zone+0x15e/0x170
 [<ffffffff811e5ef1>] kswapd+0x4f1/0xa80
 [<ffffffff811e5a00>] ? zone_reclaim+0x230/0x230
 [<ffffffff810e6882>] kthread+0xf2/0x110
 [<ffffffff810e6790>] ? kthread_create_on_node+0x220/0x220
 [<ffffffff8184803f>] ret_from_fork+0x3f/0x70
 [<ffffffff810e6790>] ? kthread_create_on_node+0x220/0x220

To quote Dave:
"
Ignoring whether reflink should be doing anything or not, that's a
"xfs_refcountbt_init_cursor() gets called both outside and inside
transactions" lockdep false positive case. The problem here is
lockdep has seen this allocation from within a transaction, hence a
GFP_NOFS allocation, and now it's seeing it in a GFP_KERNEL context.
Also note that we have an active reference to this inode.

So, because the reclaim annotations overload the interrupt level
detections and it's seen the inode ilock been taken in reclaim
("interrupt") context, this triggers a reclaim context warning where
it thinks it is unsafe to do this allocation in GFP_KERNEL context
holding the inode ilock...
"

This sounds like a fundamental problem of the reclaim lock detection.
It is really impossible to annotate such a special usecase IMHO unless
the reclaim lockup detection is reworked completely. Until then it
is much better to provide a way to add "I know what I am doing flag"
and mark problematic places. This would prevent from abusing GFP_NOFS
flag which has a runtime effect even on configurations which have
lockdep disabled.

Introduce __GFP_NOLOCKDEP flag which tells the lockdep gfp tracking to
skip the current allocation request.

While we are at it also make sure that the radix tree doesn't
accidentaly override tags stored in the upper part of the gfp_mask.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 include/linux/gfp.h      | 10 +++++++++-
 kernel/locking/lockdep.c |  4 ++++
 lib/radix-tree.c         |  2 ++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index db373b9d3223..978232a3b4ae 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -40,6 +40,11 @@  struct vm_area_struct;
 #define ___GFP_DIRECT_RECLAIM	0x400000u
 #define ___GFP_WRITE		0x800000u
 #define ___GFP_KSWAPD_RECLAIM	0x1000000u
+#ifdef CONFIG_LOCKDEP
+#define ___GFP_NOLOCKDEP	0x4000000u
+#else
+#define ___GFP_NOLOCKDEP	0
+#endif
 /* If the above are modified, __GFP_BITS_SHIFT may need updating */
 
 /*
@@ -179,8 +184,11 @@  struct vm_area_struct;
 #define __GFP_NOTRACK	((__force gfp_t)___GFP_NOTRACK)
 #define __GFP_NOTRACK_FALSE_POSITIVE (__GFP_NOTRACK)
 
+/* Disable lockdep for GFP context tracking */
+#define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP)
+
 /* Room for N __GFP_FOO bits */
-#define __GFP_BITS_SHIFT 25
+#define __GFP_BITS_SHIFT (25 + IS_ENABLED(CONFIG_LOCKDEP))
 #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
 
 /*
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 45acb86d3f56..7dc2375c3ec7 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2879,6 +2879,10 @@  static void __lockdep_trace_alloc(gfp_t gfp_mask, unsigned long flags)
 	if (DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags)))
 		return;
 
+	/* Disable lockdep if explicitly requested */
+	if (gfp_mask & __GFP_NOLOCKDEP)
+		return;
+
 	mark_held_locks(curr, RECLAIM_FS);
 }
 
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 9dc093d5ef39..7550be09f9d6 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -2274,6 +2274,8 @@  static int radix_tree_cpu_dead(unsigned int cpu)
 void __init radix_tree_init(void)
 {
 	int ret;
+
+	BUILD_BUG_ON(RADIX_TREE_MAX_TAGS + __GFP_BITS_SHIFT > 32);
 	radix_tree_node_cachep = kmem_cache_create("radix_tree_node",
 			sizeof(struct radix_tree_node), 0,
 			SLAB_PANIC | SLAB_RECLAIM_ACCOUNT,