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Subject: Re: [PATCH] x86, perf: check that current->mm alive before getting
 user callchain
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Andrey Vagin <avagin@openvz.org>
Cc: linux-kernel@vger.kernel.org, Paul Mackerras <paulus@samba.org>,
        Ingo Molnar <mingo@elte.hu>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Date: Tue, 30 Aug 2011 15:14:03 +0200
In-Reply-To: <1314693156-24131-1-git-send-email-avagin@openvz.org>
References: <1314693156-24131-1-git-send-email-avagin@openvz.org>
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On Tue, 2011-08-30 at 12:32 +0400, Andrey Vagin wrote:
> An event may occurs when mm is already released.

> Signed-off-by: Andrey Vagin <avagin@openvz.org>
> ---
>  arch/x86/kernel/cpu/perf_event.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
> index 4ee3abf..cfa62ec 100644
> --- a/arch/x86/kernel/cpu/perf_event.c
> +++ b/arch/x86/kernel/cpu/perf_event.c
> @@ -1900,6 +1900,9 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
>  
>  	perf_callchain_store(entry, regs->ip);
>  
> +	if (!current->mm)
> +		return;
> +
>  	if (perf_callchain_user32(regs, entry))
>  		return;
>  

Thanks!