linux-kernel - Re: [PATCH 2/6] oom: Get rid of sparse warnings

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Date:	Mon, 6 Feb 2012 16:33:26 -0500
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Anton Vorontsov <anton.vorontsov@...aro.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	San Mehat <san@...gle.com>, Colin Cross <ccross@...roid.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, kernel-team@...roid.com,
	linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH 2/6] oom: Get rid of sparse warnings

2012/2/6 Anton Vorontsov <anton.vorontsov@...aro.org>:
> Sparse flood makes it hard to catch newly-introduced warnings. So let's
> fix the the sparse warnings in the oom killer:
>
>  CHECK   mm/oom_kill.c
>  mm/oom_kill.c:139:20: warning: context imbalance in
>          '__find_lock_task_mm' - wrong count at exit
>  mm/oom_kill.c:771:9: warning: context imbalance in 'out_of_memory' -
>          different lock contexts for basic block
>
> The first one is fixed by assuring sparse that we know that we exit
> with the lock held.
>
> The second one is caused by the fact that sparse isn't smart enough
> to handle noreturn attribute.
>
> Signed-off-by: Anton Vorontsov <anton.vorontsov@...aro.org>
> ---
>  mm/oom_kill.c |    9 ++++++++-
>  1 files changed, 8 insertions(+), 1 deletions(-)
>
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 0ebb383..49569b6 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -142,8 +142,14 @@ struct task_struct *__find_lock_task_mm(struct task_struct *p)
>
>        do {
>                task_lock(t);
> -               if (likely(t->mm))
> +               if (likely(t->mm)) {
> +                       /*
> +                        * Shut up sparse: we do know that we exit w/ the
> +                        * task locked.
> +                        */
> +                       __release(&t->alloc_loc);

task struct only have allock_lock, not alloc_loc. Moreover we don't release
the lock in this code path. Seems odd.



>                        return t;
> +               }
>                task_unlock(t);
>        } while_each_thread(p, t);
>
> @@ -766,6 +772,7 @@ retry:
>                dump_header(NULL, gfp_mask, order, NULL, mpol_mask);
>                read_unlock(&tasklist_lock);
>                panic("Out of memory and no killable processes...\n");
> +               return;
>        }
>
>        if (oom_kill_process(p, gfp_mask, order, points, totalpages, NULL,
> --
> 1.7.7.6
>
--
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