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Date:	Thu, 20 Mar 2014 12:01:10 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.cz>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>
Subject: Re: kswapd using __this_cpu_add() in preemptible code

On Tue, Mar 18, 2014 at 02:22:16PM -0700, Andrew Morton wrote:
> On Tue, 18 Mar 2014 21:53:30 +0300 Sergey Senozhatsky <sergey.senozhatsky@...il.com> wrote:
> 
> > Hello gentlemen,
> > 
> > Commit 589a606f9539663f162e4a110d117527833b58a4 ("percpu: add preemption
> > checks to __this_cpu ops") added preempt check to used in __count_vm_events()
> > __this_cpu ops, causing the following kswapd warning:
> > 
> >  BUG: using __this_cpu_add() in preemptible [00000000] code: kswapd0/56
> >  caller is __this_cpu_preempt_check+0x2b/0x2d
> >  Call Trace:
> >  [<ffffffff813b8d4d>] dump_stack+0x4e/0x7a
> >  [<ffffffff8121366f>] check_preemption_disabled+0xce/0xdd
> >  [<ffffffff812136bb>] __this_cpu_preempt_check+0x2b/0x2d
> >  [<ffffffff810f622e>] inode_lru_isolate+0xed/0x197
> >  [<ffffffff810be43c>] list_lru_walk_node+0x7b/0x14c
> >  [<ffffffff810f6141>] ? iput+0x131/0x131
> >  [<ffffffff810f681f>] prune_icache_sb+0x35/0x4c
> >  [<ffffffff810e3951>] super_cache_scan+0xe3/0x143
> >  [<ffffffff810b1301>] shrink_slab_node+0x103/0x16f
> >  [<ffffffff810b19fd>] shrink_slab+0x75/0xe4
> >  [<ffffffff810b3f3d>] balance_pgdat+0x2fa/0x47f
> >  [<ffffffff810b4395>] kswapd+0x2d3/0x2fd
> >  [<ffffffff81068049>] ? __wake_up_sync+0xd/0xd
> >  [<ffffffff810b40c2>] ? balance_pgdat+0x47f/0x47f
> >  [<ffffffff81051e75>] kthread+0xd6/0xde
> >  [<ffffffff81051d9f>] ? kthread_create_on_node+0x162/0x162
> >  [<ffffffff813be5bc>] ret_from_fork+0x7c/0xb0
> >  [<ffffffff81051d9f>] ? kthread_create_on_node+0x162/0x162
> > 
> > 
> > list_lru_walk_node() seems to be the only place where __count_vm_events()
> > called with preemption enabled. remaining __count_vm_events() and
> > __count_vm_event() calls are done with preemption disabled (unless I
> > overlooked something).
> 
> Christoph caught one.  How does this look?
> 
> 
> 
> From: Andrew Morton <akpm@...ux-foundation.org>
> Subject: fs/inode.c:inode_lru_isolate(): use atomic count_vm_events()
> 
> "percpu: add preemption checks to __this_cpu ops" added preempt check to
> used in __count_vm_events() __this_cpu ops, causing the following kswapd
> warning:
> 
>  BUG: using __this_cpu_add() in preemptible [00000000] code: kswapd0/56
>  caller is __this_cpu_preempt_check+0x2b/0x2d
>  Call Trace:
>  [<ffffffff813b8d4d>] dump_stack+0x4e/0x7a
>  [<ffffffff8121366f>] check_preemption_disabled+0xce/0xdd
>  [<ffffffff812136bb>] __this_cpu_preempt_check+0x2b/0x2d
>  [<ffffffff810f622e>] inode_lru_isolate+0xed/0x197
>  [<ffffffff810be43c>] list_lru_walk_node+0x7b/0x14c
>  [<ffffffff810f6141>] ? iput+0x131/0x131
>  [<ffffffff810f681f>] prune_icache_sb+0x35/0x4c
> 
> Switch from __count_vm_events() to the preempt-safe count_vm_events().
> 
> Reported-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> Cc: Christoph Lameter <cl@...ux-foundation.org>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> ---
> 
>  fs/inode.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff -puN fs/inode.c~fs-inodec-inode_lru_isolate-use-atomic-count_vm_events fs/inode.c
> --- a/fs/inode.c~fs-inodec-inode_lru_isolate-use-atomic-count_vm_events
> +++ a/fs/inode.c
> @@ -722,9 +722,9 @@ inode_lru_isolate(struct list_head *item
>  			unsigned long reap;
>  			reap = invalidate_mapping_pages(&inode->i_data, 0, -1);
>  			if (current_is_kswapd())
> -				__count_vm_events(KSWAPD_INODESTEAL, reap);
> +				count_vm_events(KSWAPD_INODESTEAL, reap);
>  			else
> -				__count_vm_events(PGINODESTEAL, reap);
> +				count_vm_events(PGINODESTEAL, reap);
>  			if (current->reclaim_state)
>  				current->reclaim_state->reclaimed_slab += reap;
>  		}

Acked-by: Dave Chinner <dchinner@...hat.com>

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
--
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