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Date: Wed, 6 Dec 2017 17:39:51 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>,
        Fengguang Wu <fengguang.wu@intel.com>, linux-kernel@vger.kernel.org,
        Wang Nan <wangnan0@huawei.com>, Ingo Molnar <mingo@redhat.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Will Deacon <will.deacon@arm.com>, lkp@01.org,
        Dmitry Vyukov <dvyukov@google.com>, kasan-dev@googlegroups.com,
        kernel-team@lge.com
Subject: Re: BUG: KASAN: slab-out-of-bounds in perf_callchain_user+0x494/0x530
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On Thu, Dec 07, 2017 at 12:49:57AM +0900, Namhyung Kim wrote:

> So, are you ok with this?

yeah, that should work.

> diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
> index 1b2be63c8528..ee0ba22d3993 100644
> --- a/kernel/events/callchain.c
> +++ b/kernel/events/callchain.c
> @@ -137,8 +137,11 @@ int get_callchain_buffers(int event_max_stack)
>  
>         err = alloc_callchain_buffers();
>  exit:
> -       if (err)
> -               atomic_dec(&nr_callchain_events);
> +       if (err) {
> +               /* might race with put_callchain_buffers() */
> +               if (atomic_dec_and_test(&nr_callchain_events))
> +                       release_callchain_buffers();
> +       }
>  
>         mutex_unlock(&callchain_mutex);
>