Messages in this thread Patch in this message | | | Subject | Re: [PATCH 4/4] tracing/filters: use ring_buffer_discard_commit for discarded events | From | Tom Zanussi <> | Date | Tue, 07 Apr 2009 00:46:49 -0500 |
| |
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 >
| |