On Wed, Jan 30, 2013 at 09:42:14AM +0400, Stanislav Kinsbursky wrote: > 30.01.2013 02:57, J. Bruce Fields пишет: > >On Tue, Jan 29, 2013 at 02:03:30PM +0300, Stanislav Kinsbursky wrote: > >>There could be a service transport, which is processed by service thread and > >>racing in the same time with per-net service shutdown like listed below: > >> > >>CPU#0: CPU#1: > >> > >>svc_recv svc_close_net > >>svc_get_next_xprt (list_del_init(xpt_ready)) > >> svc_close_list (set XPT_BUSY and XPT_CLOSE) > >> svc_clear_pools(xprt was gained on CPU#0 already) > >> svc_delete_xprt (set XPT_DEAD) > >>svc_handle_xprt (is XPT_CLOSE => svc_delete_xprt() > >>BUG() > >> > >>There could be different solutions of the problem. > >>Probably, the patch doesn't implement the best one, but I hope the simple one. > >>IOW, it protects critical section (dequeuing of pending transport and > >>enqueuing it back to the pool) by per-service rw semaphore, > > > >It's actually per-thread (per-struct svc_rqst) here. > > > > Yes, sure. > > >>taken for read. > >>On per-net transports shutdown, this semaphore have to be taken for write. > > > >There's no down_write in this patch. Did you forget this part? > > > > See "fs/nfs/callback.c" part Whoops, sorry; got it.--b. > > >The server rpc code goes to some care not to write to any global > >structure, to prevent server threads running on multiple cores from > >bouncing cache lines between them. > > > > This is just an idea. I.e. I wasn't trying to polish the patch - just to share the vision. > > >But my understanding is that even down_read() does modify the semaphore. > >So we might want something like the percpu semaphore describe in > >Documentation/percpu-rw-semaphore.txt. > > > > Sure, I'll have a look. > > > -- > Best regards, > Stanislav Kinsbursky -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
