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Subject: Re: [PATCH v2 (RESEND)] lockdep: Fix fs_reclaim warning.

I assumed this patch goes to mainline via locking tree, but neither
Peter nor Ingo is responding. Andrew, can you pick up this patch?

Tetsuo Handa wrote:
> From 361d37a7d36978020dfb4c11ec1f4800937ccb68 Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <[email protected]>
> Date: Thu, 8 Feb 2018 10:35:35 +0900
> Subject: [PATCH v2] lockdep: Fix fs_reclaim warning.
>
> Dave Jones reported fs_reclaim lockdep warnings.
>
> ============================================
> WARNING: possible recursive locking detected
> 4.15.0-rc9-backup-debug+ #1 Not tainted
> --------------------------------------------
> sshd/24800 is trying to acquire lock:
> (fs_reclaim){+.+.}, at: [<0000000084f438c2>] fs_reclaim_acquire.part.102+0x5/0x30
>
> but task is already holding lock:
> (fs_reclaim){+.+.}, at: [<0000000084f438c2>] fs_reclaim_acquire.part.102+0x5/0x30
>
> other info that might help us debug this:
> Possible unsafe locking scenario:
>
> CPU0
> ----
> lock(fs_reclaim);
> lock(fs_reclaim);
>
> *** DEADLOCK ***
>
> May be due to missing lock nesting notation
>
> 2 locks held by sshd/24800:
> #0: (sk_lock-AF_INET6){+.+.}, at: [<000000001a069652>] tcp_sendmsg+0x19/0x40
> #1: (fs_reclaim){+.+.}, at: [<0000000084f438c2>] fs_reclaim_acquire.part.102+0x5/0x30
>
> stack backtrace:
> CPU: 3 PID: 24800 Comm: sshd Not tainted 4.15.0-rc9-backup-debug+ #1
> Call Trace:
> dump_stack+0xbc/0x13f
> __lock_acquire+0xa09/0x2040
> lock_acquire+0x12e/0x350
> fs_reclaim_acquire.part.102+0x29/0x30
> kmem_cache_alloc+0x3d/0x2c0
> alloc_extent_state+0xa7/0x410
> __clear_extent_bit+0x3ea/0x570
> try_release_extent_mapping+0x21a/0x260
> __btrfs_releasepage+0xb0/0x1c0
> btrfs_releasepage+0x161/0x170
> try_to_release_page+0x162/0x1c0
> shrink_page_list+0x1d5a/0x2fb0
> shrink_inactive_list+0x451/0x940
> shrink_node_memcg.constprop.88+0x4c9/0x5e0
> shrink_node+0x12d/0x260
> try_to_free_pages+0x418/0xaf0
> __alloc_pages_slowpath+0x976/0x1790
> __alloc_pages_nodemask+0x52c/0x5c0
> new_slab+0x374/0x3f0
> ___slab_alloc.constprop.81+0x47e/0x5a0
> __slab_alloc.constprop.80+0x32/0x60
> __kmalloc_track_caller+0x267/0x310
> __kmalloc_reserve.isra.40+0x29/0x80
> __alloc_skb+0xee/0x390
> sk_stream_alloc_skb+0xb8/0x340
> tcp_sendmsg_locked+0x8e6/0x1d30
> tcp_sendmsg+0x27/0x40
> inet_sendmsg+0xd0/0x310
> sock_write_iter+0x17a/0x240
> __vfs_write+0x2ab/0x380
> vfs_write+0xfb/0x260
> SyS_write+0xb6/0x140
> do_syscall_64+0x1e5/0xc05
> entry_SYSCALL64_slow_path+0x25/0x25
>
> This warning is caused by commit d92a8cfcb37ecd13 ("locking/lockdep: Rework
> FS_RECLAIM annotation") which replaced lockdep_set_current_reclaim_state()/
> lockdep_clear_current_reclaim_state() in __perform_reclaim() and
> lockdep_trace_alloc() in slab_pre_alloc_hook() with fs_reclaim_acquire()/
> fs_reclaim_release(). Since __kmalloc_reserve() from __alloc_skb() adds
> __GFP_NOMEMALLOC | __GFP_NOWARN to gfp_mask, and all reclaim path simply
> propagates __GFP_NOMEMALLOC, fs_reclaim_acquire() in slab_pre_alloc_hook()
> is trying to grab the 'fake' lock again when __perform_reclaim() already
> grabbed the 'fake' lock.
>
> The
>
> /* this guy won't enter reclaim */
> if ((current->flags & PF_MEMALLOC) && !(gfp_mask & __GFP_NOMEMALLOC))
> return false;
>
> test which causes slab_pre_alloc_hook() to try to grab the 'fake' lock
> was added by commit cf40bd16fdad42c0 ("lockdep: annotate reclaim context
> (__GFP_NOFS)"). But that test is outdated because PF_MEMALLOC thread won't
> enter reclaim regardless of __GFP_NOMEMALLOC after commit 341ce06f69abfafa
> ("page allocator: calculate the alloc_flags for allocation only once")
> added the PF_MEMALLOC safeguard (
>
> /* Avoid recursion of direct reclaim */
> if (p->flags & PF_MEMALLOC)
> goto nopage;
>
> in __alloc_pages_slowpath()).
>
> Thus, let's fix outdated test by removing __GFP_NOMEMALLOC test and allow
> __need_fs_reclaim() to return false.
>
> Reported-and-tested-by: Dave Jones <[email protected]>
> Signed-off-by: Tetsuo Handa <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: Nick Piggin <[email protected]>
> ---
> mm/page_alloc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 81e18ce..19fb76b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3590,7 +3590,7 @@ static bool __need_fs_reclaim(gfp_t gfp_mask)
> return false;
>
> /* this guy won't enter reclaim */
> - if ((current->flags & PF_MEMALLOC) && !(gfp_mask & __GFP_NOMEMALLOC))
> + if (current->flags & PF_MEMALLOC)
> return false;
>
> /* We're only interested __GFP_FS allocations for now */
> --
> 1.8.3.1
>
>

2018-03-07 23:34:17

by Andrew Morton

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Subject: Re: [PATCH v2 (RESEND)] lockdep: Fix fs_reclaim warning.

On Wed, 28 Feb 2018 06:50:02 +0900 Tetsuo Handa <[email protected]> wrote:

>
> This warning is caused by commit d92a8cfcb37ecd13 ("locking/lockdep: Rework
> FS_RECLAIM annotation") which replaced lockdep_set_current_reclaim_state()/
> lockdep_clear_current_reclaim_state() in __perform_reclaim() and
> lockdep_trace_alloc() in slab_pre_alloc_hook() with fs_reclaim_acquire()/
> fs_reclaim_release(). Since __kmalloc_reserve() from __alloc_skb() adds
> __GFP_NOMEMALLOC | __GFP_NOWARN to gfp_mask, and all reclaim path simply
> propagates __GFP_NOMEMALLOC, fs_reclaim_acquire() in slab_pre_alloc_hook()
> is trying to grab the 'fake' lock again when __perform_reclaim() already
> grabbed the 'fake' lock.

That's quite an audit trail.

Shouldn't we be doing a cc:stable here? If so, which patch do we
identify as being fixed, with "Fixes:"? d92a8cfcb37ecd13, I assume?

I'd never even noticed fs_reclaim_acquire() and friends before. I do
wish they had "lockdep" in their names, and a comment to explain what
they do and why they exist.

2018-03-08 15:32:26

by Tetsuo Handa

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Subject: Re: [PATCH v2 (RESEND)] lockdep: Fix fs_reclaim warning.

Andrew Morton wrote:
> On Wed, 28 Feb 2018 06:50:02 +0900 Tetsuo Handa <[email protected]> wrote:
>
> >
> > This warning is caused by commit d92a8cfcb37ecd13 ("locking/lockdep: Rework
> > FS_RECLAIM annotation") which replaced lockdep_set_current_reclaim_state()/
> > lockdep_clear_current_reclaim_state() in __perform_reclaim() and
> > lockdep_trace_alloc() in slab_pre_alloc_hook() with fs_reclaim_acquire()/
> > fs_reclaim_release(). Since __kmalloc_reserve() from __alloc_skb() adds
> > __GFP_NOMEMALLOC | __GFP_NOWARN to gfp_mask, and all reclaim path simply
> > propagates __GFP_NOMEMALLOC, fs_reclaim_acquire() in slab_pre_alloc_hook()
> > is trying to grab the 'fake' lock again when __perform_reclaim() already
> > grabbed the 'fake' lock.
>
> That's quite an audit trail.
>
> Shouldn't we be doing a cc:stable here? If so, which patch do we
> identify as being fixed, with "Fixes:"? d92a8cfcb37ecd13, I assume?

Yes please, if you think this patch qualifies for backport.

The test was outdated since v2.6.31, but only v4.14+ seems to trigger this warning.
Thus, I think it is OK to add:

Fixes: d92a8cfcb37ecd13 ("locking/lockdep: Rework FS_RECLAIM annotation")
Cc: <[email protected]> # v4.14+

>
> I'd never even noticed fs_reclaim_acquire() and friends before. I do
> wish they had "lockdep" in their names, and a comment to explain what
> they do and why they exist.