[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <1239083209.7220.42.camel@tropicana>
Date: Tue, 07 Apr 2009 00:46:49 -0500
From: Tom Zanussi <tzanussi@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 4/4] tracing/filters: use ring_buffer_discard_commit
for discarded events
On Thu, 2009-04-02 at 11:01 -0400, Steven Rostedt wrote:
> On Thu, 2 Apr 2009, Tom Zanussi wrote:
>
> > Hi Steve,
> >
> > Great to see this! I updated my filter removal rcu patch, made some
> > changes to the filter_check_discard() to work with the new
> > ring_buffer_discard_commit() and made the necessary changes to the
> > ftrace tracers as well - see the patch below, which has only been
> > touch-tested at this point. It seemed to work at first, but then
> > produced an oops, which may well be a problem related to the changes I
> > made. I'll look into it more tomorrow night, and will also fix up this
> > patch and repost it if it basically looks ok. I'll post the oops and
> > the lines of code that it refers to just in case it it rings a bell...
>
> Yeah, it looks like it is related to changes that you made ;-)
>
> >
> > [ 240.461982] ------------[ cut here ]------------
> > [ 240.461993] WARNING: at kernel/trace/ring_buffer.c:1610
> > ring_buffer_discard_commit+0xfa/0x100()
>
> > [ 240.462259] Pid: 6143, comm: bash Not tainted 2.6.29-tip #35
> > [ 240.462267] Call Trace:
> > [ 240.462280] [<ffffffff8025c5c8>] warn_slowpath+0xd8/0x130
> > [ 240.462291] [<ffffffff802c2be5>] ? rb_reserve_next_event+0x45/0x360
> > [ 240.462304] [<ffffffff802c6fc1>] ? trace_buffer_lock_reserve
> > +0x51/0x70
> > [ 240.462316] [<ffffffff802c12ea>] ? ring_buffer_unlock_commit
> > +0x5a/0x60
> > [ 240.462329] [<ffffffff802c2be5>] ? rb_reserve_next_event+0x45/0x360
> > [ 240.462340] [<ffffffff802c30cb>] ? ring_buffer_lock_reserve
> > +0x9b/0xe0
> > [ 240.462354] [<ffffffff8035f42b>] ? dnotify_parent+0xb/0xc0
> > [ 240.462365] [<ffffffff8032af65>] ? vfs_write+0x155/0x1d0
> > [ 240.462375] [<ffffffff802c1e2a>] ring_buffer_discard_commit
> > +0xfa/0x100
> > [ 240.462386] [<ffffffff8035f42b>] ? dnotify_parent+0xb/0xc0
> > [ 240.462396] [<ffffffff802c843b>] trace_function+0xab/0xc0
[...]
> The bug does not stick out in this patch set. Perhaps it is part of the
> original too? But something somewhere is calling the discard outside the
> reserve and commit.
>
It doesn't stick out to me either - the funny thing is that it only
happens with CONFIG_PREEMPT_VOLUNTARY - with CONFIG_PREEMPT it's fine.
In fact, with CONFIG_PREEMPT_VOLUNTARY, an RB_WARN_ON(!preempt_count())
right after frace_preempt_disable() triggers immediately, which unless
I'm missing something, should never happen. Is there a bug in
PREEMPT_VOLUNTARY?
Tom
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 7a6209f..bac9ab7 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1494,6 +1494,8 @@ ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
/* If we are tracing schedule, we don't want to recurse */
resched = ftrace_preempt_disable();
+ RB_WARN_ON(buffer, !preempt_count());
+
cpu = raw_smp_processor_id();
if (!cpumask_test_cpu(cpu, buffer->cpumask))
> -- Steve
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists