From: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Subject: 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.
Link: http://lkml.kernel.org/r/201802280650.FJC73911.FOSOMLJVFFQtHO@I-love.SAKURA.... Fixes: d92a8cfcb37ecd13 ("locking/lockdep: Rework FS_RECLAIM annotation") Signed-off-by: Tetsuo Handa penguin-kernel@I-love.SAKURA.ne.jp Reported-by: Dave Jones davej@codemonkey.org.uk Tested-by: Dave Jones davej@codemonkey.org.uk Cc: Peter Zijlstra peterz@infradead.org Cc: Nick Piggin npiggin@gmail.com Cc: Ingo Molnar mingo@elte.hu Cc: Nikolay Borisov nborisov@suse.com Cc: Michal Hocko mhocko@kernel.org Cc: stable@vger.kernel.org [4.14+] Signed-off-by: Andrew Morton <> ---
mm/page_alloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN mm/page_alloc.c~lockdep-fix-fs_reclaim-warning mm/page_alloc.c --- a/mm/page_alloc.c~lockdep-fix-fs_reclaim-warning +++ a/mm/page_alloc.c @@ -3596,7 +3596,7 @@ static bool __need_fs_reclaim(gfp_t gfp_ 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 */ _