diff options
| -rw-r--r-- | fs/eventpoll.c | 25 |
1 files changed, 18 insertions, 7 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 9026fc91fe3b..828e750af23a 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -70,6 +70,15 @@ * simultaneous inserts (A into B and B into A) from racing and * constructing a cycle without either insert observing that it is * going to. + * It is necessary to acquire multiple "ep->mtx"es at once in the + * case when one epoll fd is added to another. In this case, we + * always acquire the locks in the order of nesting (i.e. after + * epoll_ctl(e1, EPOLL_CTL_ADD, e2), e1->mtx will always be acquired + * before e2->mtx). Since we disallow cycles of epoll file + * descriptors, this ensures that the mutexes are well-ordered. In + * order to communicate this nesting to lockdep, when walking a tree + * of epoll file descriptors, we use the current recursion depth as + * the lockdep subkey. * It is possible to drop the "ep->mtx" and to use the global * mutex "epmutex" (together with "ep->lock") to have it working, * but having "ep->mtx" will make the interface more scalable. @@ -464,13 +473,15 @@ static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi) * @ep: Pointer to the epoll private data structure. * @sproc: Pointer to the scan callback. * @priv: Private opaque data passed to the @sproc callback. + * @depth: The current depth of recursive f_op->poll calls. * * Returns: The same integer error code returned by the @sproc callback. */ static int ep_scan_ready_list(struct eventpoll *ep, int (*sproc)(struct eventpoll *, struct list_head *, void *), - void *priv) + void *priv, + int depth) { int error, pwake = 0; unsigned long flags; @@ -481,7 +492,7 @@ static int ep_scan_ready_list(struct eventpoll *ep, * We need to lock this because we could be hit by * eventpoll_release_file() and epoll_ctl(). */ - mutex_lock(&ep->mtx); + mutex_lock_nested(&ep->mtx, depth); /* * Steal the ready list, and re-init the original one to the @@ -670,7 +681,7 @@ static int ep_read_events_proc(struct eventpoll *ep, struct list_head *head, static int ep_poll_readyevents_proc(void *priv, void *cookie, int call_nests) { - return ep_scan_ready_list(priv, ep_read_events_proc, NULL); + return ep_scan_ready_list(priv, ep_read_events_proc, NULL, call_nests + 1); } static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait) @@ -737,7 +748,7 @@ void eventpoll_release_file(struct file *file) ep = epi->ep; list_del_init(&epi->fllink); - mutex_lock(&ep->mtx); + mutex_lock_nested(&ep->mtx, 0); ep_remove(ep, epi); mutex_unlock(&ep->mtx); } @@ -1134,7 +1145,7 @@ static int ep_send_events(struct eventpoll *ep, esed.maxevents = maxevents; esed.events = events; - return ep_scan_ready_list(ep, ep_send_events_proc, &esed); + return ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0); } static inline struct timespec ep_set_mstimeout(long ms) @@ -1267,7 +1278,7 @@ static int ep_loop_check_proc(void *priv, void *cookie, int call_nests) struct rb_node *rbp; struct epitem *epi; - mutex_lock(&ep->mtx); + mutex_lock_nested(&ep->mtx, call_nests + 1); for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) { epi = rb_entry(rbp, struct epitem, rbn); if (unlikely(is_file_epoll(epi->ffd.file))) { @@ -1409,7 +1420,7 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd, } - mutex_lock(&ep->mtx); + mutex_lock_nested(&ep->mtx, 0); /* * Try to lookup the file inside our RB tree, Since we grabbed "mtx" |