From: Andrew Morton <akpm@linux-foundation.org>
To: Robert Love <rlove@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Shankar Brahadeeswaran <shankoo77@gmail.com>,
Dan Carpenter <dan.carpenter@oracle.com>,
LKML <linux-kernel@vger.kernel.org>,
Bjorn Bringert <bringert@google.com>,
devel <devel@driverdev.osuosl.org>,
Hugh Dickins <hughd@google.com>,
Anjana V Kumar <anjanavk12@gmail.com>,
linux-next <linux-next@vger.kernel.org>
Subject: Re: [PATCH -next] ashmem: Fix ashmem_shrink deadlock.
Date: Tue, 7 May 2013 13:52:30 -0700 [thread overview]
Message-ID: <20130507135230.ba90c299a79be635ef768a2a@linux-foundation.org> (raw)
In-Reply-To: <1367416573-5430-1-git-send-email-rlove@google.com>
On Wed, 1 May 2013 09:56:13 -0400 Robert Love <rlove@google.com> wrote:
> Don't acquire ashmem_mutex in ashmem_shrink if we've somehow recursed into the
> shrinker code from within ashmem. Just bail out, avoiding a deadlock. This is
> fine, as ashmem cache pruning is advisory anyhow.
>
Sorry, but I don't think "somehow" is an adequate description of a
kernel bug. The deadlock should be described with specificity, so that
others can understand and review the fix and perhaps suggest
alternative implementations.
Presumably someone is performing a memory allocation while holding
ashmem_mutex. A more idiomatic way of avoiding a call to direct
reclaim in these circumstances would be for the task to set its
PF_MEMALLOC flag, or to use GFP_ATOMIC. But without any details that's
as far as I can go.
> --- a/drivers/staging/android/ashmem.c
> +++ b/drivers/staging/android/ashmem.c
> @@ -363,7 +363,11 @@ static int ashmem_shrink(struct shrinker *s, struct shrink_control *sc)
> if (!sc->nr_to_scan)
> return lru_count;
>
> - mutex_lock(&ashmem_mutex);
> + /* avoid recursing into this code from within ashmem itself */
> + if (!mutex_trylock(&ashmem_mutex)) {
> + return -1;
> + }
This is rather hacky. It consumes more CPU than the above approaches,
and more stack.
Worst of all, it obviously hasn't met checkpatch.pl ;)
next prev parent reply other threads:[~2013-05-07 20:52 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-01 13:56 [PATCH -next] ashmem: Fix ashmem_shrink deadlock Robert Love
2013-05-01 15:54 ` David Rientjes
2013-05-02 18:22 ` David Rientjes
2013-05-02 20:39 ` Greg Kroah-Hartman
2013-05-07 20:52 ` Andrew Morton [this message]
2013-05-13 21:42 ` Greg Kroah-Hartman
2013-05-14 3:29 ` Neil Zhang
2013-05-14 3:37 ` Raul Xiong
2013-05-16 8:15 ` Raul Xiong
2013-05-16 13:44 ` Robert Love
2013-05-16 16:45 ` Andrew Morton
2013-05-16 17:08 ` Robert Love
2013-05-16 17:19 ` Andrew Morton
2013-05-16 17:28 ` Robert Love
2013-09-17 5:05 ` Raul Xiong
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