From: Steven Rostedt <rostedt@goodmis.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Glauber de Oliveira Costa <gcosta@redhat.com>,
Chris Wright <chrisw@sous-sol.org>,
Jeremy Fitzhardinge <jeremy@goop.org>,
Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: [PATCH 0/2] [GIT PULL] tracing: various bug fixes
Date: Wed, 22 Apr 2009 09:49:14 -0400 (EDT) [thread overview]
Message-ID: <alpine.DEB.2.00.0904220943280.24310@gandalf.stny.rr.com> (raw)
In-Reply-To: <20090422114750.GA14202@nowhere>
On Wed, 22 Apr 2009, Frederic Weisbecker wrote:
> >
> > I spent the entire day (and half the night) debugging this. I was fighting
> > a case where the hardirqs_enabled flag in the task struct (lockdep flag)
> > was mysteriously being set and cleared. I stepped through the entire
> > kernel thread fork process (that was an exercise) and could not find
> > anything wrong.
> >
> > Sometimes it would go away with printk's sometimes it would not. This was
> > driving me crazy, until I noticed that paravirt was enabled.
> >
> > Turning off paravirtualization here (so far) makes everything run
> > smoothly.
> >
> > Thus my theory is that there's something fishy with the modifying of the
> > irq enable/disable code when the system detects that it is running on bare
> > hardware.
> >
> > I'm too tired to look at this more. Ingo supplied a config to play with.
> > You can disable VSMP too and it will still trigger the crash.
> >
> > -- Steve
> >
>
> It's indeed a tricky one. I can reproduce it too, I will
> try to manage having an irqsoff trace at this point, hopefully I
> could get the source of this irq disabling...
It doesn't disable interrupts :-/
It is the hardirqs_enabled flag in the task struct that mysteriously turns
off and back on. I put in printks when it is off in fork, and the next
printk shows that it turns back on (between the printks!!!).
I printed the output of "irqs_disabled()" on each of these printks and
interrupts are always enabled. It is only the hardirqs_enabled flag that
is giving strange outputs.
Do you have CONFIG_PARAVIRT on? When I disabled it, I have yet to
reproduce the bug. But I've only rebooted a few times. I'm going to
continue to reboot to see if I can trigger it.
I'm thinking that the paravirt alternative code may have clobbered a
register in either the enable or disabling of interrupts. This might cause
a strange value to go into the hardirqs_enabled flag.
Thanks,
-- Steve
next prev parent reply other threads:[~2009-04-22 13:49 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-04-20 22:22 [PATCH 0/2] [GIT PULL] tracing: various bug fixes Steven Rostedt
2009-04-20 22:22 ` [PATCH 1/2] tracing: use recursive counter over irq level Steven Rostedt
2009-04-20 22:22 ` [PATCH 2/2] tracing: use nowakeup version of commit for function event trace tests Steven Rostedt
2009-04-20 22:41 ` Frederic Weisbecker
2009-04-20 22:57 ` Steven Rostedt
2009-04-21 8:23 ` [PATCH 0/2] [GIT PULL] tracing: various bug fixes Ingo Molnar
2009-04-21 9:46 ` Ingo Molnar
2009-04-21 13:08 ` Steven Rostedt
2009-04-21 13:55 ` [PATCH][GIT PULL] ring-buffer: only warn on wrap if buffer is bigger than two pages Steven Rostedt
2009-04-21 14:35 ` Ingo Molnar
2009-04-21 14:54 ` Steven Rostedt
2009-04-21 16:22 ` Steven Rostedt
2009-04-21 14:03 ` [tip:tracing/core] " tip-bot for Steven Rostedt
2009-04-22 6:48 ` [PATCH 0/2] [GIT PULL] tracing: various bug fixes Steven Rostedt
2009-04-22 11:47 ` Frederic Weisbecker
2009-04-22 13:49 ` Steven Rostedt [this message]
2009-04-22 17:10 ` Frederic Weisbecker
2009-04-22 17:17 ` Jeremy Fitzhardinge
2009-04-22 17:22 ` Steven Rostedt
2009-04-22 21:32 ` Steven Rostedt
2009-04-23 8:28 ` Ingo Molnar
2009-04-23 3:35 ` Steven Rostedt
2009-04-23 8:20 ` Ingo Molnar
2009-04-23 13:53 ` Steven Rostedt
2009-04-23 14:39 ` Steven Rostedt
2009-04-23 15:08 ` Steven Rostedt
2009-04-23 15:11 ` Ingo Molnar
2009-04-23 16:49 ` Jeremy Fitzhardinge
2009-04-23 17:21 ` Chris Wright
2009-04-23 18:02 ` Chris Wright
2009-04-23 18:33 ` Steven Rostedt
2009-04-23 18:43 ` Chris Wright
2009-04-24 8:36 ` Ingo Molnar
2009-04-24 15:12 ` Chris Wright
2009-04-29 6:16 ` [tip:tracing/core] x86: use native register access for native tlb flushing tip-bot for Chris Wright
2009-04-23 17:52 ` [PATCH 0/2] [GIT PULL] tracing: various bug fixes Steven Rostedt
2009-04-24 8:34 ` Ingo Molnar
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