linux-kernel - Re: [PATCH 3/3] tracing: Fix recursive user stack trace

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Date:	Fri, 12 Nov 2010 16:21:11 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH 3/3] tracing: Fix recursive user stack trace

Le vendredi 12 novembre 2010 à 10:10 -0500, Steven Rostedt a écrit :
> pièce jointe document texte brut
> (0003-tracing-Fix-recursive-user-stack-trace.patch)
> From: Steven Rostedt <srostedt@...hat.com>
> 
> The user stack trace can fault when examining the trace. Which
> would call the do_page_fault handler, which would trace again,
> which would do the user stack trace, which would fault and call
> do_page_fault again ...
> 
> Thus this is causing a recursive bug. We need to have a recursion
> detector here.
> 
> [ Resubmitted by Jiri Olsa ]
> Signed-off-by: Jiri Olsa <jolsa@...hat.com>
> LKML-Reference: <1289390172-9730-3-git-send-email-jolsa@...hat.com>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
>  kernel/trace/trace.c |   19 +++++++++++++++++++
>  1 files changed, 19 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 82d9b81..0215e87 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -1284,6 +1284,8 @@ void trace_dump_stack(void)
>  	__ftrace_trace_stack(global_trace.buffer, flags, 3, preempt_count());
>  }
>  
> +static DEFINE_PER_CPU(int, user_stack_count);
> +
>  void
>  ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc)
>  {
> @@ -1302,6 +1304,18 @@ ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc)
>  	if (unlikely(in_nmi()))
>  		return;
>  
> +	/*
> +	 * prevent recursion, since the user stack tracing may
> +	 * trigger other kernel events.
> +	 */
> +	preempt_disable();
> +	if (__get_cpu_var(user_stack_count))
> +		goto out;
> +

	if (__this_cpu_read(user_stack_count))
		goto out;

> +	__get_cpu_var(user_stack_count)++;

	__this_cpu_inc(user_stack_count);

> +
> +
> +
>  	event = trace_buffer_lock_reserve(buffer, TRACE_USER_STACK,
>  					  sizeof(*entry), flags, pc);
>  	if (!event)
> @@ -1319,6 +1333,11 @@ ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc)
>  	save_stack_trace_user(&trace);
>  	if (!filter_check_discard(call, entry, buffer, event))
>  		ring_buffer_unlock_commit(buffer, event);
> +
> +	__get_cpu_var(user_stack_count)--;
	__this_cpu_dec(user_stack_count);

> +
> + out:
> +	preempt_enable();
>  }
>  
>  #ifdef UNUSED


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