lkml.org 
[lkml]   [2018]   [Jan]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
SubjectRe: [4.15-rc9] fs_reclaim lockdep trace
From
Date
Dave, would you try below patch?



From cae2cbf389ae3cdef1b492622722b4aeb07eb284 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Sun, 28 Jan 2018 14:17:14 +0900
Subject: [PATCH] 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

Since no fs locks are held, doing GFP_KERNEL allocation should be safe
as long as there is PF_MEMALLOC safeguard (

/* Avoid recursion of direct reclaim */
if (p->flags & PF_MEMALLOC)
goto nopage;

) which prevents infinite recursion.

This warning seems to be caused by commit d92a8cfcb37ecd13
("locking/lockdep: Rework FS_RECLAIM annotation") which moved the
location of

/* this guy won't enter reclaim */
if ((current->flags & PF_MEMALLOC) && !(gfp_mask & __GFP_NOMEMALLOC))
return false;

check added by commit cf40bd16fdad42c0 ("lockdep: annotate reclaim context
(__GFP_NOFS)"). Since __kmalloc_reserve() from __alloc_skb() adds
__GFP_NOMEMALLOC | __GFP_NOWARN to gfp_mask, __need_fs_reclaim() is
failing to return false despite PF_MEMALLOC context (and resulted in
lockdep warning).

Since there was no PF_MEMALLOC safeguard as of cf40bd16fdad42c0, checking
__GFP_NOMEMALLOC might make sense. But since this safeguard was added by
commit 341ce06f69abfafa ("page allocator: calculate the alloc_flags for
allocation only once"), checking __GFP_NOMEMALLOC no longer makes sense.
Thus, let's remove __GFP_NOMEMALLOC check and allow __need_fs_reclaim() to
return false.

Reported-by: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Nick Piggin <npiggin@gmail.com>
---
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 76c9688..7804b0e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3583,7 +3583,7 @@ 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
\
 
 \ /
  Last update: 2018-01-28 06:56    [W:0.079 / U:1.208 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site