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

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Date:	Mon, 20 Dec 2010 20:33:59 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Li Zefan <lizf@...fujitsu.com>
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

On Tue, 2010-12-21 at 08:55 +0800, Li Zefan wrote:
> Any comment?

oops, this was buried in my email. I'll look at it tomorrow.

-- Steve

> 
> 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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