1 files changed, 99 insertions, 48 deletions

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 810c28fb8c3c..79b65c3b9e87 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -41,6 +41,7 @@
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
 #include <linux/compat.h>
+#include <linux/rculist.h>
 
 /*
  * LOCKING:
@@ -133,8 +134,12 @@ struct nested_calls {
  * of these on a server and we do not want this to take another cache line.
  */
 struct epitem {
-	/* RB tree node used to link this structure to the eventpoll RB tree */
-	struct rb_node rbn;
+	union {
+		/* RB tree node links this structure to the eventpoll RB tree */
+		struct rb_node rbn;
+		/* Used to free the struct epitem */
+		struct rcu_head rcu;
+	};
 
 	/* List header used to link this structure to the eventpoll ready list */
 	struct list_head rdllink;
@@ -580,14 +585,14 @@ static inline void ep_pm_stay_awake_rcu(struct epitem *epi)
  * @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.
+ * @ep_locked: caller already holds ep->mtx
  *
  * 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,
-			      int depth)
+			      void *priv, int depth, bool ep_locked)
 {
 	int error, pwake = 0;
 	unsigned long flags;
@@ -598,7 +603,9 @@ 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_nested(&ep->mtx, depth);
+
+	if (!ep_locked)
+		mutex_lock_nested(&ep->mtx, depth);
 
 	/*
 	 * Steal the ready list, and re-init the original one to the
@@ -662,7 +669,8 @@ static int ep_scan_ready_list(struct eventpoll *ep,
 	}
 	spin_unlock_irqrestore(&ep->lock, flags);
 
-	mutex_unlock(&ep->mtx);
+	if (!ep_locked)
+		mutex_unlock(&ep->mtx);
 
 	/* We have to call this outside the lock */
 	if (pwake)
@@ -671,6 +679,12 @@ static int ep_scan_ready_list(struct eventpoll *ep,
 	return error;
 }
 
+static void epi_rcu_free(struct rcu_head *head)
+{
+	struct epitem *epi = container_of(head, struct epitem, rcu);
+	kmem_cache_free(epi_cache, epi);
+}
+
 /*
  * Removes a "struct epitem" from the eventpoll RB tree and deallocates
  * all the associated resources. Must be called with "mtx" held.
@@ -692,8 +706,7 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi)
 
 	/* Remove the current item from the list of epoll hooks */
 	spin_lock(&file->f_lock);
-	if (ep_is_linked(&epi->fllink))
-		list_del_init(&epi->fllink);
+	list_del_rcu(&epi->fllink);
 	spin_unlock(&file->f_lock);
 
 	rb_erase(&epi->rbn, &ep->rbr);
@@ -704,9 +717,14 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi)
 	spin_unlock_irqrestore(&ep->lock, flags);
 
 	wakeup_source_unregister(ep_wakeup_source(epi));
-
-	/* At this point it is safe to free the eventpoll item */
-	kmem_cache_free(epi_cache, epi);
+	/*
+	 * At this point it is safe to free the eventpoll item. Use the union
+	 * field epi->rcu, since we are trying to minimize the size of
+	 * 'struct epitem'. The 'rbn' field is no longer in use. Protected by
+	 * ep->mtx. The rcu read side, reverse_path_check_proc(), does not make
+	 * use of the rbn field.
+	 */
+	call_rcu(&epi->rcu, epi_rcu_free);
 
 	atomic_long_dec(&ep->user->epoll_watches);
 
@@ -807,15 +825,34 @@ static int ep_read_events_proc(struct eventpoll *ep, struct list_head *head,
 	return 0;
 }
 
+static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
+				 poll_table *pt);
+
+struct readyevents_arg {
+	struct eventpoll *ep;
+	bool locked;
+};
+
 static int ep_poll_readyevents_proc(void *priv, void *cookie, int call_nests)
 {
-	return ep_scan_ready_list(priv, ep_read_events_proc, NULL, call_nests + 1);
+	struct readyevents_arg *arg = priv;
+
+	return ep_scan_ready_list(arg->ep, ep_read_events_proc, NULL,
+				  call_nests + 1, arg->locked);
 }
 
 static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait)
 {
 	int pollflags;
 	struct eventpoll *ep = file->private_data;
+	struct readyevents_arg arg;
+
+	/*
+	 * During ep_insert() we already hold the ep->mtx for the tfile.
+	 * Prevent re-aquisition.
+	 */
+	arg.locked = wait && (wait->_qproc == ep_ptable_queue_proc);
+	arg.ep = ep;
 
 	/* Insert inside our poll wait queue */
 	poll_wait(file, &ep->poll_wait, wait);
@@ -827,7 +864,7 @@ static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait)
 	 * could re-enter here.
 	 */
 	pollflags = ep_call_nested(&poll_readywalk_ncalls, EP_MAX_NESTS,
-				   ep_poll_readyevents_proc, ep, ep, current);
+				   ep_poll_readyevents_proc, &arg, ep, current);
 
 	return pollflags != -1 ? pollflags : 0;
 }
@@ -872,7 +909,6 @@ static const struct file_operations eventpoll_fops = {
  */
 void eventpoll_release_file(struct file *file)
 {
-	struct list_head *lsthead = &file->f_ep_links;
 	struct eventpoll *ep;
 	struct epitem *epi;
 
@@ -890,17 +926,12 @@ void eventpoll_release_file(struct file *file)
 	 * Besides, ep_remove() acquires the lock, so we can't hold it here.
 	 */
 	mutex_lock(&epmutex);
-
-	while (!list_empty(lsthead)) {
-		epi = list_first_entry(lsthead, struct epitem, fllink);
-
+	list_for_each_entry_rcu(epi, &file->f_ep_links, fllink) {
 		ep = epi->ep;
-		list_del_init(&epi->fllink);
 		mutex_lock_nested(&ep->mtx, 0);
 		ep_remove(ep, epi);
 		mutex_unlock(&ep->mtx);
 	}
-
 	mutex_unlock(&epmutex);
 }
 
@@ -1138,7 +1169,9 @@ static int reverse_path_check_proc(void *priv, void *cookie, int call_nests)
 	struct file *child_file;
 	struct epitem *epi;
 
-	list_for_each_entry(epi, &file->f_ep_links, fllink) {
+	/* CTL_DEL can remove links here, but that can't increase our count */
+	rcu_read_lock();
+	list_for_each_entry_rcu(epi, &file->f_ep_links, fllink) {
 		child_file = epi->ep->file;
 		if (is_file_epoll(child_file)) {
 			if (list_empty(&child_file->f_ep_links)) {
@@ -1160,6 +1193,7 @@ static int reverse_path_check_proc(void *priv, void *cookie, int call_nests)
 				"file is not an ep!\n");
 		}
 	}
+	rcu_read_unlock();
 	return error;
 }
 
@@ -1231,7 +1265,7 @@ static noinline void ep_destroy_wakeup_source(struct epitem *epi)
  * Must be called with "mtx" held.
  */
 static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
-		     struct file *tfile, int fd)
+		     struct file *tfile, int fd, int full_check)
 {
 	int error, revents, pwake = 0;
 	unsigned long flags;
@@ -1286,7 +1320,7 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
 
 	/* Add the current item to the list of active epoll hook for this file */
 	spin_lock(&tfile->f_lock);
-	list_add_tail(&epi->fllink, &tfile->f_ep_links);
+	list_add_tail_rcu(&epi->fllink, &tfile->f_ep_links);
 	spin_unlock(&tfile->f_lock);
 
 	/*
@@ -1297,7 +1331,7 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
 
 	/* now check if we've created too many backpaths */
 	error = -EINVAL;
-	if (reverse_path_check())
+	if (full_check && reverse_path_check())
 		goto error_remove_epi;
 
 	/* We have to drop the new item inside our item list to keep track of it */
@@ -1327,8 +1361,7 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
 
 error_remove_epi:
 	spin_lock(&tfile->f_lock);
-	if (ep_is_linked(&epi->fllink))
-		list_del_init(&epi->fllink);
+	list_del_rcu(&epi->fllink);
 	spin_unlock(&tfile->f_lock);
 
 	rb_erase(&epi->rbn, &ep->rbr);
@@ -1521,7 +1554,7 @@ 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, 0);
+	return ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0, false);
 }
 
 static inline struct timespec ep_set_mstimeout(long ms)
@@ -1791,11 +1824,12 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
 		struct epoll_event __user *, event)
 {
 	int error;
-	int did_lock_epmutex = 0;
+	int full_check = 0;
 	struct fd f, tf;
 	struct eventpoll *ep;
 	struct epitem *epi;
 	struct epoll_event epds;
+	struct eventpoll *tep = NULL;
 
 	error = -EFAULT;
 	if (ep_op_has_event(op) &&
@@ -1814,7 +1848,7 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
 
 	/* The target file descriptor must support poll */
 	error = -EPERM;
-	if (!tf.file->f_op || !tf.file->f_op->poll)
+	if (!tf.file->f_op->poll)
 		goto error_tgt_fput;
 
 	/* Check if EPOLLWAKEUP is allowed */
@@ -1844,26 +1878,40 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
 	 * and hang them on the tfile_check_list, so we can check that we
 	 * haven't created too many possible wakeup paths.
 	 *
-	 * We need to hold the epmutex across both ep_insert and ep_remove
-	 * b/c we want to make sure we are looking at a coherent view of
-	 * epoll network.
+	 * We do not need to take the global 'epumutex' on EPOLL_CTL_ADD when
+	 * the epoll file descriptor is attaching directly to a wakeup source,
+	 * unless the epoll file descriptor is nested. The purpose of taking the
+	 * 'epmutex' on add is to prevent complex toplogies such as loops and
+	 * deep wakeup paths from forming in parallel through multiple
+	 * EPOLL_CTL_ADD operations.
 	 */
-	if (op == EPOLL_CTL_ADD || op == EPOLL_CTL_DEL) {
-		mutex_lock(&epmutex);
-		did_lock_epmutex = 1;
-	}
+	mutex_lock_nested(&ep->mtx, 0);
 	if (op == EPOLL_CTL_ADD) {
-		if (is_file_epoll(tf.file)) {
-			error = -ELOOP;
-			if (ep_loop_check(ep, tf.file) != 0) {
-				clear_tfile_check_list();
-				goto error_tgt_fput;
+		if (!list_empty(&f.file->f_ep_links) ||
+						is_file_epoll(tf.file)) {
+			full_check = 1;
+			mutex_unlock(&ep->mtx);
+			mutex_lock(&epmutex);
+			if (is_file_epoll(tf.file)) {
+				error = -ELOOP;
+				if (ep_loop_check(ep, tf.file) != 0) {
+					clear_tfile_check_list();
+					goto error_tgt_fput;
+				}
+			} else
+				list_add(&tf.file->f_tfile_llink,
+							&tfile_check_list);
+			mutex_lock_nested(&ep->mtx, 0);
+			if (is_file_epoll(tf.file)) {
+				tep = tf.file->private_data;
+				mutex_lock_nested(&tep->mtx, 1);
 			}
-		} else
-			list_add(&tf.file->f_tfile_llink, &tfile_check_list);
+		}
+	}
+	if (op == EPOLL_CTL_DEL && is_file_epoll(tf.file)) {
+		tep = tf.file->private_data;
+		mutex_lock_nested(&tep->mtx, 1);
 	}
-
-	mutex_lock_nested(&ep->mtx, 0);
 
 	/*
 	 * Try to lookup the file inside our RB tree, Since we grabbed "mtx"
@@ -1877,10 +1925,11 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
 	case EPOLL_CTL_ADD:
 		if (!epi) {
 			epds.events |= POLLERR | POLLHUP;
-			error = ep_insert(ep, &epds, tf.file, fd);
+			error = ep_insert(ep, &epds, tf.file, fd, full_check);
 		} else
 			error = -EEXIST;
-		clear_tfile_check_list();
+		if (full_check)
+			clear_tfile_check_list();
 		break;
 	case EPOLL_CTL_DEL:
 		if (epi)
@@ -1896,10 +1945,12 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
 			error = -ENOENT;
 		break;
 	}
+	if (tep != NULL)
+		mutex_unlock(&tep->mtx);
 	mutex_unlock(&ep->mtx);
 
 error_tgt_fput:
-	if (did_lock_epmutex)
+	if (full_check)
 		mutex_unlock(&epmutex);
 
 	fdput(tf);