Re: Re: Re: [PATCH v3 0/5] ARM64: Add kernel probes(Kprobes) support
(2014/11/29 1:01), Steve Capper wrote:
> On 27 November 2014 at 06:07, Masami Hiramatsu
> wrote:
>> (2014/11/27 3:59), Steve Capper wrote:
>>> 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;
}
> 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,
>
> David,
> Does the above make sense to you? Have you managed to reproduce the crash I
> get?
>
> Cheers,
> --
> Steve
> --
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>
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu...@hitachi.com
--
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Re: Re: Re: [PATCH v3 0/5] ARM64: Add kernel probes(Kprobes) support
(2014/11/29 1:01), Steve Capper wrote:
On 27 November 2014 at 06:07, Masami Hiramatsu
masami.hiramatsu...@hitachi.com wrote:
(2014/11/27 3:59), Steve Capper wrote:
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;
}
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,
David,
Does the above make sense to you? Have you managed to reproduce the crash I
get?
Cheers,
--
Steve
--
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu...@hitachi.com
--
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
