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-rw-r--r--fs/eventpoll.c45
1 files changed, 40 insertions, 5 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 2a7dcd6ddc09..739b0985b398 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -426,6 +426,31 @@ out_unlock:
return error;
}
+/*
+ * As described in commit 0ccf831cb lockdep: annotate epoll
+ * the use of wait queues used by epoll is done in a very controlled
+ * manner. Wake ups can nest inside each other, but are never done
+ * with the same locking. For example:
+ *
+ * dfd = socket(...);
+ * efd1 = epoll_create();
+ * efd2 = epoll_create();
+ * epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...);
+ * epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...);
+ *
+ * When a packet arrives to the device underneath "dfd", the net code will
+ * issue a wake_up() on its poll wake list. Epoll (efd1) has installed a
+ * callback wakeup entry on that queue, and the wake_up() performed by the
+ * "dfd" net code will end up in ep_poll_callback(). At this point epoll
+ * (efd1) notices that it may have some event ready, so it needs to wake up
+ * the waiters on its poll wait list (efd2). So it calls ep_poll_safewake()
+ * that ends up in another wake_up(), after having checked about the
+ * recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to
+ * avoid stack blasting.
+ *
+ * When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle
+ * this special case of epoll.
+ */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
static inline void ep_wake_up_nested(wait_queue_head_t *wqueue,
unsigned long events, int subclass)
@@ -698,9 +723,12 @@ static int ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
void *priv)
{
struct epitem *epi, *tmp;
+ poll_table pt;
+ init_poll_funcptr(&pt, NULL);
list_for_each_entry_safe(epi, tmp, head, rdllink) {
- if (epi->ffd.file->f_op->poll(epi->ffd.file, NULL) &
+ pt._key = epi->event.events;
+ if (epi->ffd.file->f_op->poll(epi->ffd.file, &pt) &
epi->event.events)
return POLLIN | POLLRDNORM;
else {
@@ -1048,13 +1076,11 @@ static int reverse_path_check_proc(void *priv, void *cookie, int call_nests)
*/
static int reverse_path_check(void)
{
- int length = 0;
int error = 0;
struct file *current_file;
/* let's call this for all tfiles */
list_for_each_entry(current_file, &tfile_check_list, f_tfile_llink) {
- length++;
path_count_init();
error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS,
reverse_path_check_proc, current_file,
@@ -1096,6 +1122,7 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
/* Initialize the poll table using the queue callback */
epq.epi = epi;
init_poll_funcptr(&epq.pt, ep_ptable_queue_proc);
+ epq.pt._key = event->events;
/*
* Attach the item to the poll hooks and get current event bits.
@@ -1190,6 +1217,9 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even
{
int pwake = 0;
unsigned int revents;
+ poll_table pt;
+
+ init_poll_funcptr(&pt, NULL);
/*
* Set the new event interest mask before calling f_op->poll();
@@ -1197,13 +1227,14 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even
* f_op->poll() call and the new event set registering.
*/
epi->event.events = event->events;
+ pt._key = event->events;
epi->event.data = event->data; /* protected by mtx */
/*
* Get current event bits. We can safely use the file* here because
* its usage count has been increased by the caller of this function.
*/
- revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);
+ revents = epi->ffd.file->f_op->poll(epi->ffd.file, &pt);
/*
* If the item is "hot" and it is not registered inside the ready
@@ -1238,6 +1269,9 @@ static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
unsigned int revents;
struct epitem *epi;
struct epoll_event __user *uevent;
+ poll_table pt;
+
+ init_poll_funcptr(&pt, NULL);
/*
* We can loop without lock because we are passed a task private list.
@@ -1250,7 +1284,8 @@ static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
list_del_init(&epi->rdllink);
- revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL) &
+ pt._key = epi->event.events;
+ revents = epi->ffd.file->f_op->poll(epi->ffd.file, &pt) &
epi->event.events;
/*