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SubjectRe: [PATCH 2/2] tracing/events/lockdep: move tracepoints within recursive protection


On Fri, 17 Apr 2009, Mathieu Desnoyers wrote:
> > ---[ end trace 03d889e04bc7a9a7 ]---
> > possible reason: unannotated irqs-on.
> > irq event stamp: 12569
> > hardirqs last enabled at (12567): [<ffffffff8026206a>] local_bh_enable+0xaa/0x110
> > hardirqs last disabled at (12569): [<ffffffff80610c76>] int3+0x16/0x40
> > softirqs last enabled at (12566): [<ffffffff80514d2b>] lock_sock_nested+0xfb/0x110
> > softirqs last disabled at (12568): [<ffffffff8058454e>] tcp_prequeue_process+0x2e/0xa0
> >
> >
> > Note, for some reason we hit int3 ??
> >
> > Tracepoints do not use int3 does it?
> >
>
> Not in your ftrace tree. My LTTng tree includes the immediate values,
> which brienfly uses the int3 handler when enabling/disabling
> tracepoints. But this seems unrelated to your problem.

Maybe something else is adding it :-/

>
> > I have kprobes defined but not any kprobe self tests on.
> >
>
> Could this be a userspace breakpoint then ?

Nope, it happens right in the kernel. And the path I describe below points
out that we have a bug in irq tracing when we take a int3 in kernel space.

>
> > Anyway, let me describe what the above is and what I found in my
> > investigation.
> >
> > The lockdep took a check_flags error when it noticed that interrupts were
> > enabled, but the current->hardirqs_enabled was 0. Lockdep thought
> > interrupts were disabled but they were in fact enabled.
> >
> >
> > The last 4 lines of the warning have the numbers in the parenthesis
> > annotate the order of events: (Here they are in order)
> >
> > softirqs last enabled at (12566): [<ffffffff80514d2b>] lock_sock_nested+0xfb/0x110
> > hardirqs last enabled at (12567): [<ffffffff8026206a>] local_bh_enable+0xaa/0x110
> > softirqs last disabled at (12568): [<ffffffff8058454e>] tcp_prequeue_process+0x2e/0xa0
> > hardirqs last disabled at (12569): [<ffffffff80610c76>] int3+0x16/0x40
> >
> > The last change that lockdep saw was interrupts being disabled by int3. I
> > still don't understand why int3 was enabled. I have startup tests for
> > ftrace and the event tracer, but this blob happened when I first ssh'd
> > into the box.
>
> Also note that maybe some entry.S annotation could be missing, making
> kallsyms think it was running within int3 when in fact it was running in
> a different function. I would double-check with objdump givin the
> ffffffff80610c76 address to make sure.

Actually, that was the first thing I did. Because I thought int3 was
weird.


>
> Just giving my 2 cents before going to bed. I don't have any more brain
> left for tonight.

Thanks,

-- Steve


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