diff options
Diffstat (limited to 'epoll-fix-spurious-lockdep-warnings.patch')
| -rw-r--r-- | epoll-fix-spurious-lockdep-warnings.patch | 116 |
1 files changed, 116 insertions, 0 deletions
diff --git a/epoll-fix-spurious-lockdep-warnings.patch b/epoll-fix-spurious-lockdep-warnings.patch new file mode 100644 index 000000000..c163a86d7 --- /dev/null +++ b/epoll-fix-spurious-lockdep-warnings.patch @@ -0,0 +1,116 @@ +epoll can acquire multiple ep->mutex on multiple "struct eventpoll"s +at once in the case where one epoll fd is monitoring another epoll +fd. This is perfectly OK, since we're careful about the lock ordering, +but causes spurious lockdep warnings. Annotate the recursion using +mutex_lock_nested, and add a comment explaining the nesting rules for +good measure. + +Reported-by: Paul Bolle <pebolle@tiscali.nl> +Signed-off-by: Nelson Elhage <nelhage@nelhage.com> +--- + I've tested this on a synthetic epoll test case, that just adds e1 to + e2 and then does an epoll_wait(). I verified that it caused lockdep + problems on 3.0 and that this patch fixed it, but I haven't done more + extensive testing. Paul, are you able to test systemd against this? + + fs/eventpoll.c | 25 ++++++++++++++++++------- + 1 files changed, 18 insertions(+), 7 deletions(-) + +diff --git a/fs/eventpoll.c b/fs/eventpoll.c +index f9cfd16..0cb7bc6 100644 +--- a/fs/eventpoll.c ++++ b/fs/eventpoll.c +@@ -76,6 +76,15 @@ + * Events that require holding "epmutex" are very rare, while for + * normal operations the epoll private "ep->mtx" will guarantee + * a better scalability. ++ * It is possible 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. + */ + + /* Epoll private bits inside the event mask */ +@@ -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" +-- +1.7.4.1 + +-- +To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in +the body of a message to majordomo@vger.kernel.org +More majordomo info at http://vger.kernel.org/majordomo-info.html |