On Mon, Mar 25, 2019 at 11:52:17AM -0700, Omar Sandoval wrote: > On Fri, Mar 22, 2019 at 09:13:51AM +0800, Ming Lei wrote: > > Inside sbitmap_queue_clear(), once the clear bit is set, it will be > > visiable to allocation path immediately. Meantime READ/WRITE on old > > associated instance(such as request in case of blk-mq) may be > > out-of-order with the setting clear bit, so race with re-allocation > > may be triggered. > > > > Adds one memory barrier for ordering READ/WRITE of the freed associated > > instance with setting clear bit for avoiding race with re-allocation. > > Just to make sure I understand, the race is something like this? > > Thread 1 Thread 2 > sbitmap_queue_get() > ... > write to request _____ > sbitmap_queue_clear() \ > \ sbitmap_queue_get() > \______ observes write > > If so, you can add > > Reviewed-by: Omar Sandoval <osandov@xxxxxx> Yeah, it is one normal race between freeing and allocating. Thanks, Ming
