Re: [PATCH for tip][bugfix] ftrace: fix deadlock when setting set_ftrace_pid

Ingo Molnar
2009-03-06T11:08:23Z

* Lai Jiangshan <laijs@cn.fujitsu.com> wrote:

> KOSAKI Motohiro wrote:
> > Impact: fix deadlock bug
> >
> > reproduce way:
> > # cd /sys/kernel/debug/tracing
> > # echo $$ > set_ftrace_pid
> >
> > then, console become hangup.
> >
> > detail:
> > when writing set_ftracepid, kernel callstack is following
> >
> > ftrace_pid_write()
> > mutex_lock(&ftrace_lock);
> > ftrace_update_pid_func()
> > mutex_lock(&ftrace_lock);
> > mutex_unlock(&ftrace_lock);
> > mutex_unlock(&ftrace_lock);
> >
> > then, system alaways deadlock when ftrace_pid_write() is called.
> >
> > In past days, ftrace_pid_write() use ftrace_start_lock, but
> > commit e6ea44e9b4c12325337cd1c06103cd515a1c02b2 consolidate
> > ftrace_start_lock to ftrace_lock.
> >
> >
> > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> > ---
> > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > index 5a3a06b..0d3b393 100644
> > --- a/kernel/trace/ftrace.c
> > +++ b/kernel/trace/ftrace.c
> > @@ -218,10 +218,8 @@ static void ftrace_update_pid_func(void)
> > {
> > ftrace_func_t func;
> >
> > - mutex_lock(&ftrace_lock);
> > -
> > if (ftrace_trace_function == ftrace_stub)
> > - goto out;
> > + return;
> >
> > func = ftrace_trace_function;
> >
> > @@ -238,9 +236,6 @@ static void ftrace_update_pid_func(void)
> > #else
> > __ftrace_trace_function = func;
> > #endif
> > -
> > - out:
> > - mutex_unlock(&ftrace_lock);
> > }
> >
> > /* set when tracing only a pid */
> >
> >
>
> Reviewed-By: Lai Jiangshan <laijs@cn.fujitsu.com>

Applied, thanks!

Ingo