From: Steven Rostedt <rostedt@goodmis.org>
To: Li Zefan <lizf@cn.fujitsu.com>
Cc: Jiri Olsa <jolsa@redhat.com>,
mingo@elte.hu, andi@firstfloor.org, lwoodman@redhat.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] tracing - fix recursive user stack trace
Date: Thu, 11 Nov 2010 16:57:04 -0500 [thread overview]
Message-ID: <1289512624.12418.350.camel@gandalf.stny.rr.com> (raw)
In-Reply-To: <4CDB3538.4080605@cn.fujitsu.com>
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
next prev parent reply other threads:[~2010-11-11 21:57 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-10 11:56 [PATCH 0/2] tracing,mm - add kernel pagefault tracepoint for x86 & x86_64 Jiri Olsa
2010-11-10 11:56 ` [PATCH 1/2] " Jiri Olsa
2010-11-10 13:29 ` Christoph Hellwig
2010-11-10 13:44 ` Jiri Olsa
2010-11-10 13:52 ` Ingo Molnar
2010-11-10 15:00 ` Frederic Weisbecker
2010-11-10 15:17 ` Jiri Olsa
2010-11-10 15:20 ` Christoph Hellwig
2010-11-10 16:28 ` Andi Kleen
2010-11-10 16:44 ` Frederic Weisbecker
2010-11-11 9:09 ` [PATCHv2 0/2] " Jiri Olsa
2010-11-11 9:09 ` [PATCHv2 1/2] tracing - fix recursive user stack trace Jiri Olsa
2010-11-11 10:34 ` Andi Kleen
2010-11-11 9:09 ` [PATCHv2 2/2] tracing,mm - add kernel pagefault tracepoint for x86 & x86_64 Jiri Olsa
2010-11-11 12:51 ` Christoph Hellwig
2010-11-11 13:15 ` Jiri Olsa
2010-11-15 13:43 ` Frederic Weisbecker
2010-11-15 14:06 ` Andi Kleen
2010-11-15 14:54 ` Frederic Weisbecker
2010-11-15 15:04 ` Steven Rostedt
2010-11-15 14:19 ` Steven Rostedt
2010-11-16 9:23 ` Jiri Olsa
2010-11-16 13:13 ` Steven Rostedt
2010-11-10 11:56 ` [PATCH 2/2] tracing - fix recursive user stack trace Jiri Olsa
2010-11-11 0:13 ` Li Zefan
2010-11-11 21:57 ` Steven Rostedt [this message]
2010-11-18 14:05 ` [tip:perf/core] tracing: Fix " tip-bot for Steven Rostedt
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1289512624.12418.350.camel@gandalf.stny.rr.com \
--to=rostedt@goodmis.org \
--cc=andi@firstfloor.org \
--cc=jolsa@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=lizf@cn.fujitsu.com \
--cc=lwoodman@redhat.com \
--cc=mingo@elte.hu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).