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SubjectRe: [PATCH v7 06/16] lockdep: Detect and handle hist_lock ring buffer overwrite
On Thu, Jul 13, 2017 at 7:29 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, Jul 13, 2017 at 07:09:53PM +0900, Byungchul Park wrote:
>> On Thu, Jul 13, 2017 at 11:50:52AM +0200, Peter Zijlstra wrote:
>> > wait_for_completion(&C);
>> > atomic_inc_return();
>> >
>> > mutex_lock(A1);
>> > mutex_unlock(A1);
>> >
>> >
>> > <IRQ>
>> > spin_lock(B1);
>> > spin_unlock(B1);
>> >
>> > ...
>> >
>> > spin_lock(B64);
>> > spin_unlock(B64);
>> > </IRQ>
>> >
>> >
>> > mutex_lock(A2);
>> > mutex_unlock(A2);
>> >
>> > complete(&C);
>> >
>> >
>> > That gives:
>> >
>> > xhist[ 0] = A1
>>
>> We have to rollback here later on irq_exit.
>>
>> The followings are ones for irq context.
>>
>> > xhist[ 1] = B1
>> > ...
>> > xhist[63] = B63
>> >
>> > then we wrap and have:
>> >
>> > xhist[0] = B64
>> >
>> > then we rewind to 1 and invalidate to arrive at:
>> >
>>
>> Now, whether xhist[0] has been overwritten or not is important. If yes,
>> xhist[0] should be NULL, _not_ xhist[1], which is one for irq context so
>> not interest at all.
>>
>> > xhist[ 0] = B64
>> > xhist[ 1] = NULL <-- idx
>>
>> Therefore, it should be,
>>
>> xhist[ 0] = NULL <- invalidate, cannot use it any more
>> --- <- on returning back from irq context, start from here
>> xhist[ 1] = B1 <-- obsolete history of irq
>
> Ah, so you rely on the same_context_xhlock() ? That doesn't work for
> hist (formerly work).

As I mentioned in cover-letter, I applied the rollback mechanism into work
(of workqueue) as well. So it works even for hist.

--
Thanks,
Byungchul

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