Re: WARNING in percpu_ref_kill_and_confirm

Jens Axboe
2019-04-22T16:50:56Z

On 4/22/19 10:48 AM, Linus Torvalds wrote:
> On Mon, Apr 22, 2019 at 9:38 AM Jens Axboe <axboe@kernel.dk> wrote:
>>
>> With the mutex change in, I can trigger it in a second or so. Just ran
>> the reproducer with that change reverted, and I'm not seeing any badness.
>> So I do wonder if the bisect results are accurate?
>
> Looking at the syzbot report, it's syzbot being confused.
>
> The actual WARNING in percpu_ref_kill_and_confirm() only happens with
> recent kernels.
>
> But then syzbot mixes it up with a completely different bug:
>
> crash: BUG: MAX_STACK_TRACE_ENTRIES too low!
> BUG: MAX_STACK_TRACE_ENTRIES too low!
>
> and for some reason decides that *that* bug is the same thing entirely.
>
> So yeah, I think the simple percpu_ref_is_dying() check is sufficient,
> and that the syzbot bisection is completely bogus.

Ah good, that makes me feel better. I'll queue the fix up, thanks.

--
Jens Axboe