On 5/1/18 10:06 AM, Linus Torvalds wrote: > On Tue, May 1, 2018 at 3:27 AM Tetsuo Handa < > penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote: > >> Can you review this patch? syzbot has hit this bug for nearly 4000 times > but >> is still unable to find a reproducer. Therefore, the only way to test > would be >> to apply this patch upstream and test whether the problem is solved. > > Looks ok to me, except: > >>> smp_wmb(); >>> clear_bit(WB_shutting_down, &wb->state); >>> + smp_mb(); /* advised by wake_up_bit() */ >>> + wake_up_bit(&wb->state, WB_shutting_down); > > This whole sequence really should just be a pattern with a helper function. > > And honestly, the pattern probably *should* be > > clear_bit_unlock(bit, &mem); > smp_mb__after_atomic() > wake_up_bit(&mem, bit); > > which looks like it is a bit cleaner wrt memory ordering rules. Agree, that construct looks saner than introducing a "random" smp_mb(). As a pattern helper, should probably be introduced after the fact. -- Jens Axboe
