On 12/01/2014 04:37 AM, Masami Hiramatsu wrote:

(2014/11/29 1:01), Steve Capper wrote:

quoted

On 27 November 2014 at 06:07, Masami Hiramatsu
[off-list ref] wrote:

quoted

(2014/11/27 3:59), Steve Capper wrote:

quoted

The crash is extremely easy to reproduce.

I've not observed any missed events on a kprobe on an arm64 system
that's still alive.
My (limited!) understanding is that this suggests there could be a
problem with how missed events from a recursive call to memcpy are
being handled.

I think so too. BTW, could you bisect that? :)

I can't bisect, but the following functions look suspicious to me
(again I'm new to kprobes...):
kprobes_save_local_irqflag
kprobes_restore_local_irqflag

I think these are breaking somehow when nested (i.e. from a recursive probe).

Agreed. On x86, prev_kprobe has old_flags and saved_flags, this
at least must have saved_irqflag and save/restore it in
save/restore_previous_kprobe().

What about adding this?

 struct prev_kprobe {
 	struct kprobe *kp;
 	unsigned int status;
+	unsigned long saved_irqflag;
 };

and

 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 {
 	kcb->prev_kprobe.kp = kprobe_running();
 	kcb->prev_kprobe.status = kcb->kprobe_status;
+	kcb->prev_kprobe.saved_irqflag = kcb->saved_irqflag;
 }

 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 {
 	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 	kcb->kprobe_status = kcb->prev_kprobe.status;
+	kcb->saved_irqflag = kcb->prev_kprobe.saved_irqflag;
 }

I have noticed with the aarch64 kprobe patches and recent kernel I can get the machine to end up getting stuck and printing out endless strings of

[187694.855843] Unexpected kernel single-step exception at EL1
[187694.861385] Unexpected kernel single-step exception at EL1
[187694.866926] Unexpected kernel single-step exception at EL1
[187694.872467] Unexpected kernel single-step exception at EL1
[187694.878009] Unexpected kernel single-step exception at EL1
[187694.883550] Unexpected kernel single-step exception at EL1

I can reproduce this pretty easily on my machine with functioncallcount.stp from https://sourceware.org/systemtap/examples/profiling/functioncallcount.stp and the following steps:

# stap -p4 -k -m mm_probes -w functioncallcount.stp "*@mm/*.c" -c "sleep 1"
# staprun mm_probes.ko -c "sleep 1"

-Will

quoted

That would explain why the state of play of the interrupts is in an
unexpected state in the crash I reported:
"The point of failure in the panic was:
fs/buffer.c:1257

static inline void check_irqs_on(void)
{
#ifdef irqs_disabled
        BUG_ON(irqs_disabled());
#endif
}
"

This is all new to me so I'm still at the head-scratching stage.

Ah, I see.

Thank you,

quoted

David,
Does the above make sense to you? Have you managed to reproduce the crash I get?

Cheers,
--
Steve
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