Messages in this thread | | | Subject | Re: [PATCH 2/2] tracing - fix recursive user stack trace | From | Steven Rostedt <> | Date | Thu, 11 Nov 2010 16:57:04 -0500 |
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On Thu, 2010-11-11 at 08:13 +0800, Li Zefan wrote: > Jiri Olsa wrote: > > 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. > > > > I guess this is from what I reported to Redhat, triggered by > the ftrace stress test. ;) > > This patch should be the first patch, otherwise you introduce > a regression. Though it merely a problem in this case, better > avoid it.
Yeah, this should go into urgent, and the other patch can be queued for 38.
> > A nitpick below: > > > > > Signed-off-by: Steven Rostedt <srostedt@redhat.com> > > Signed-off-by: Jiri Olsa <jolsa@redhat.com> > > --- > > 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; > > + > > + __get_cpu_var(user_stack_count)++; > > + > > + > > + > > redundant blank lines.
I can pull this patch with the fix.
Thanks!
-- Steve
> > > 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)--; > > + > > + out: > > + preempt_enable(); > > } > > > > #ifdef UNUSED
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