On Thu, Aug 30, 2018 at 02:46:16PM +0000, Eugeniy Paltsev wrote:

On Thu, 2018-08-30 at 16:17 +0200, Peter Zijlstra wrote:

quoted

On Thu, Aug 30, 2018 at 11:53:17AM +0000, Eugeniy Paltsev wrote:

quoted

I can see crashes with LLSC enabled in both SMP running on 4 cores
and SMP running on 1 core.

So you're running on LL/SC enabled hardware; that would make Will's
patch irrelevant (although still a good idea for the hardware that does
care about that spinlocked atomic crud).

Does something like the below cure things? That would confirm the
suggestion that the change to __clear_bit_unlock() is the curprit.

I tested it - this doesn't change anything, the problem still reproduces.

OK, 'good' :-)

I'll test it with last Will fix.

Yes, that missing "bnz 1b" is very very suspect.