linux-kernel - Re: [PATCH] tracing: Fix preempt count leak

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Message-ID: <4D0FFB1A.7070407@cn.fujitsu.com>
Date:	Tue, 21 Dec 2010 08:55:54 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Hiroyuki KAMEZAWA <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH] tracing: Fix preempt count leak

Any comment?

15:47, Li Zefan wrote:
> While running my ftrace stress test, this showed up:
> 
> BUG: sleeping function called from invalid context at mm/mmap.c:233
> ...
> note: cat[3293] exited with preempt_count 1
> 
> The bug was introduced by commit 91e86e560d0b3ce4c5fc64fd2bbb99f856a30a4e
> ("tracing: Fix recursive user stack trace")
> 
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> ---
>  kernel/trace/trace.c |    6 ++----
>  1 files changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index c380612..5767457 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -1313,12 +1313,10 @@ ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc)
>  
>  	__this_cpu_inc(user_stack_count);
>  
> -
> -
>  	event = trace_buffer_lock_reserve(buffer, TRACE_USER_STACK,
>  					  sizeof(*entry), flags, pc);
>  	if (!event)
> -		return;
> +		goto out_drop_count;
>  	entry	= ring_buffer_event_data(event);
>  
>  	entry->tgid		= current->tgid;
> @@ -1333,8 +1331,8 @@ ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc)
>  	if (!filter_check_discard(call, entry, buffer, event))
>  		ring_buffer_unlock_commit(buffer, event);
>  
> + out_drop_count:
>  	__this_cpu_dec(user_stack_count);
> -
>   out:
>  	preempt_enable();
>  }
--
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