[PATCH] x86 entry_64.S lockdep fix

[Mathieu Desnoyers]

* Steven Rostedt (rostedt@xxxxxxxxxxx) wrote:
> 
> 
> 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

I happened to have the following patch hanging around in my LTTng tree
for a while. Would it solve your problem by any chance ? I had to move
it a bit around in my patchset to put it before the nmi-safe int3
handler patch I have, but it should apply correctly.


x86 entry_64.S lockdep fix

Add missing lockdep irq on instrumentation to entry_64.S.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
---
 arch/x86/kernel/entry_64.S |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6-lttng/arch/x86/kernel/entry_64.S
===================================================================
--- linux-2.6-lttng.orig/arch/x86/kernel/entry_64.S	2009-04-17 17:44:18.000000000 -0400
+++ linux-2.6-lttng/arch/x86/kernel/entry_64.S	2009-04-17 17:53:42.000000000 -0400
@@ -1420,9 +1420,9 @@ ENTRY(paranoid_exit)
 	testl $3,CS(%rsp)
 	jnz   paranoid_userspace
 paranoid_swapgs:
-	TRACE_IRQS_IRETQ 0
 	SWAPGS_UNSAFE_STACK
 paranoid_restore:
+	TRACE_IRQS_IRETQ 0
 	RESTORE_ALL 8
 	jmp irq_return
 paranoid_userspace:

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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