(2014/08/01 20:00), Ingo Molnar wrote:
>
> * Masami Hiramatsu <masami.hiramatsu...@hitachi.com> wrote:
>
>> Skip kretprobe hit in NMI context, because if an NMI happens
>> inside the critical section protected by kretprobe_table.lock
>> and another(or same) kretprobe hit, pre_kretprobe_handler
>> tries to lock kretprobe_table.lock again.
>> Normal interrupts have no problem because they are disabled
>> with the lock.
>>
>> Signed-off-by: Masami Hiramatsu <masami.hiramatsu...@hitachi.com>
>> Cc: Ananth N Mavinakayanahalli <ana...@in.ibm.com>
>> Cc: "David S. Miller" <da...@davemloft.net>
>> ---
>> kernel/kprobes.c | 6 ++++++
>> 1 file changed, 6 insertions(+)
>>
>> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
>> index 734e9a7..a537029 100644
>> --- a/kernel/kprobes.c
>> +++ b/kernel/kprobes.c
>> @@ -1778,6 +1778,12 @@ static int pre_handler_kretprobe(struct kprobe *p,
>> struct pt_regs *regs)
>> unsigned long hash, flags = 0;
>> struct kretprobe_instance *ri;
>>
>> + /* To avoid deadlock, prohibit return probing in NMI context */
>> + if (in_nmi()) {
>
> Should be unlikely()?
Ah, Indeed.
>
>> + rp->nmissed++;
>> + return 0;
>
> In another place in this function we do:
>
> } else {
> rp->nmissed++;
> raw_spin_unlock_irqrestore(&rp->lock, flags);
> }
>
> Is it safe to modify rp-> without locking?
Yes, rp->nmissed is just for noticing the fault to users,
not for controlling.:) If we need more accurate value, we'd
better make it atomic_t.
Thank you,
>
>> + }
>> +
>> /*TODO: consider to only swap the RA after the last pre_handler fired */
>
> Nit: That comment is oddly formatted.
>
> Thanks,
>
> Ingo
>
--
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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