On Thu, Jan 20, 2011 at 3:50 AM, Jan Kara <jack@xxxxxxx> wrote: > On Thu 20-01-11 03:03:23, Nick Piggin wrote: >> On Thu, Jan 20, 2011 at 12:21 AM, Jan Kara <jack@xxxxxxx> wrote: >> > Well, we are not required to cancel all the outstanding AIO because of the >> > API requirement, that's granted. But we must do it because of the way how >> > the code is written. Outstanding IO requests reference ioctx but they are >> > not counted in ctx->users but in ctx->reqs_active. So the code relies on >> > the fact that the reference held by the hash table protects ctx from being >> > freed and io_destroy() waits for requests before dropping the last >> > reference to ctx. But there's the second race I describe making it possible >> > for new IO to be created after io_destroy() has waited for all IO to >> > finish... >> >> Yes there is that race too I agree. I just didn't follow through the code far >> enough to see it was a problem -- I thought it was by design. >> >> I'd like to solve it without synchronize_rcu() though. > Ah, OK. I don't find io_destroy() performance critical but I can Probably not performance critical, but it could be a very large slowdown so somebody might complain. > understand that you need not like synchronize_rcu() there. ;) Then it > should be possible to make IO requests count in ctx->users which would > solve the race as well. We'd just have to be prepared that request > completion might put the last reference to ioctx and free it but that > shouldn't be an issue. Do you like that solution better? I think so, if it can be done without slowing things down and adding locks or atomics if possible. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
