1 files changed, 304 insertions, 207 deletions

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index c5c424f23fd5..8a23a91e1377 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1,6 +1,6 @@
 /*
- *  fs/eventpoll.c (Efficent event polling implementation)
- *  Copyright (C) 2001,...,2007  Davide Libenzi
+ *  fs/eventpoll.c (Efficient event retrieval implementation)
+ *  Copyright (C) 2001,...,2009  Davide Libenzi
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -92,8 +92,8 @@
 /* Epoll private bits inside the event mask */
 #define EP_PRIVATE_BITS (EPOLLONESHOT | EPOLLET)
 
-/* Maximum number of poll wake up nests we are allowing */
-#define EP_MAX_POLLWAKE_NESTS 4
+/* Maximum number of nesting allowed inside epoll sets */
+#define EP_MAX_NESTS 4
 
 /* Maximum msec timeout value storeable in a long int */
 #define EP_MAX_MSTIMEO min(1000ULL * MAX_SCHEDULE_TIMEOUT / HZ, (LONG_MAX - 999ULL) / HZ)
@@ -110,24 +110,21 @@ struct epoll_filefd {
 };
 
 /*
- * Node that is linked into the "wake_task_list" member of the "struct poll_safewake".
- * It is used to keep track on all tasks that are currently inside the wake_up() code
- * to 1) short-circuit the one coming from the same task and same wait queue head
- * (loop) 2) allow a maximum number of epoll descriptors inclusion nesting
- * 3) let go the ones coming from other tasks.
+ * Structure used to track possible nested calls, for too deep recursions
+ * and loop cycles.
  */
-struct wake_task_node {
+struct nested_call_node {
         struct list_head llink;
         struct task_struct *task;
-        wait_queue_head_t *wq;
+        void *cookie;
 };
 
 /*
- * This is used to implement the safe poll wake up avoiding to reenter
- * the poll callback from inside wake_up().
+ * This structure is used as collector for nested calls, to check for
+ * maximum recursion dept and loop cycles.
  */
-struct poll_safewake {
-        struct list_head wake_task_list;
+struct nested_calls {
+        struct list_head tasks_call_list;
         spinlock_t lock;
 };
 
@@ -231,6 +228,12 @@ struct ep_pqueue {
         struct epitem *epi;
 };
 
+/* Used by the ep_send_events() function as callback private data */
+struct ep_send_events_data {
+        int maxevents;
+        struct epoll_event __user *events;
+};
+
 /*
  * Configuration options available inside /proc/sys/fs/epoll/
  */
@@ -242,8 +245,11 @@ static int max_user_watches __read_mostly;
  */
 static DEFINE_MUTEX(epmutex);
 
-/* Safe wake up implementation */
-static struct poll_safewake psw;
+/* Used for safe wake up implementation */
+static struct nested_calls poll_safewake_ncalls;
+
+/* Used to call file's f_op->poll() under the nested calls boundaries */
+static struct nested_calls poll_readywalk_ncalls;
 
 /* Slab cache used to allocate "struct epitem" */
 static struct kmem_cache *epi_cache __read_mostly;
@@ -312,64 +318,96 @@ static inline int ep_op_has_event(int op)
 }
 
 /* Initialize the poll safe wake up structure */
-static void ep_poll_safewake_init(struct poll_safewake *psw)
+static void ep_nested_calls_init(struct nested_calls *ncalls)
 {
-
-        INIT_LIST_HEAD(&psw->wake_task_list);
-        spin_lock_init(&psw->lock);
+        INIT_LIST_HEAD(&ncalls->tasks_call_list);
+        spin_lock_init(&ncalls->lock);
 }
 
-/*
- * Perform a safe wake up of the poll wait list. The problem is that
- * with the new callback'd wake up system, it is possible that the
- * poll callback is reentered from inside the call to wake_up() done
- * on the poll wait queue head. The rule is that we cannot reenter the
- * wake up code from the same task more than EP_MAX_POLLWAKE_NESTS times,
- * and we cannot reenter the same wait queue head at all. This will
- * enable to have a hierarchy of epoll file descriptor of no more than
- * EP_MAX_POLLWAKE_NESTS deep. We need the irq version of the spin lock
- * because this one gets called by the poll callback, that in turn is called
- * from inside a wake_up(), that might be called from irq context.
+/**
+ * ep_call_nested - Perform a bound (possibly) nested call, by checking
+ *                  that the recursion limit is not exceeded, and that
+ *                  the same nested call (by the meaning of same cookie) is
+ *                  no re-entered.
+ *
+ * @ncalls: Pointer to the nested_calls structure to be used for this call.
+ * @max_nests: Maximum number of allowed nesting calls.
+ * @nproc: Nested call core function pointer.
+ * @priv: Opaque data to be passed to the @nproc callback.
+ * @cookie: Cookie to be used to identify this nested call.
+ *
+ * Returns: Returns the code returned by the @nproc callback, or -1 if
+ *          the maximum recursion limit has been exceeded.
  */
-static void ep_poll_safewake(struct poll_safewake *psw, wait_queue_head_t *wq)
+static int ep_call_nested(struct nested_calls *ncalls, int max_nests,
+                          int (*nproc)(void *, void *, int), void *priv,
+                          void *cookie)
 {
-        int wake_nests = 0;
+        int error, call_nests = 0;
         unsigned long flags;
         struct task_struct *this_task = current;
-        struct list_head *lsthead = &psw->wake_task_list;
-        struct wake_task_node *tncur;
-        struct wake_task_node tnode;
+        struct list_head *lsthead = &ncalls->tasks_call_list;
+        struct nested_call_node *tncur;
+        struct nested_call_node tnode;
 
-        spin_lock_irqsave(&psw->lock, flags);
+        spin_lock_irqsave(&ncalls->lock, flags);
 
-        /* Try to see if the current task is already inside this wakeup call */
+        /*
+         * Try to see if the current task is already inside this wakeup call.
+         * We use a list here, since the population inside this set is always
+         * very much limited.
+         */
         list_for_each_entry(tncur, lsthead, llink) {
-
-                if (tncur->wq == wq ||
-                    (tncur->task == this_task && ++wake_nests > EP_MAX_POLLWAKE_NESTS)) {
+                if (tncur->task == this_task &&
+                    (tncur->cookie == cookie || ++call_nests > max_nests)) {
                         /*
                          * Ops ... loop detected or maximum nest level reached.
                          * We abort this wake by breaking the cycle itself.
                          */
-                        spin_unlock_irqrestore(&psw->lock, flags);
-                        return;
+                        spin_unlock_irqrestore(&ncalls->lock, flags);
+
+                        return -1;
                 }
         }
 
-        /* Add the current task to the list */
+        /* Add the current task and cookie to the list */
         tnode.task = this_task;
-        tnode.wq = wq;
+        tnode.cookie = cookie;
         list_add(&tnode.llink, lsthead);
 
-        spin_unlock_irqrestore(&psw->lock, flags);
+        spin_unlock_irqrestore(&ncalls->lock, flags);
 
-        /* Do really wake up now */
-        wake_up_nested(wq, 1 + wake_nests);
+        /* Call the nested function */
+        error = (*nproc)(priv, cookie, call_nests);
 
         /* Remove the current task from the list */
-        spin_lock_irqsave(&psw->lock, flags);
+        spin_lock_irqsave(&ncalls->lock, flags);
         list_del(&tnode.llink);
-        spin_unlock_irqrestore(&psw->lock, flags);
+        spin_unlock_irqrestore(&ncalls->lock, flags);
+
+        return error;
+}
+
+static int ep_poll_wakeup_proc(void *priv, void *cookie, int call_nests)
+{
+        wake_up_nested((wait_queue_head_t *) cookie, 1 + call_nests);
+        return 0;
+}
+
+/*
+ * Perform a safe wake up of the poll wait list. The problem is that
+ * with the new callback'd wake up system, it is possible that the
+ * poll callback is reentered from inside the call to wake_up() done
+ * on the poll wait queue head. The rule is that we cannot reenter the
+ * wake up code from the same task more than EP_MAX_NESTS times,
+ * and we cannot reenter the same wait queue head at all. This will
+ * enable to have a hierarchy of epoll file descriptor of no more than
+ * EP_MAX_NESTS deep.
+ */
+static void ep_poll_safewake(wait_queue_head_t *wq)
+{
+        ep_call_nested(&poll_safewake_ncalls, EP_MAX_NESTS,
+                       ep_poll_wakeup_proc, NULL, wq);
 }
 
 /*
@@ -397,6 +435,104 @@ static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
         }
 }
 
+/**
+ * ep_scan_ready_list - Scans the ready list in a way that makes possible for
+ *                      the scan code, to call f_op->poll(). Also allows for
+ *                      O(NumReady) performance.
+ *
+ * @ep: Pointer to the epoll private data structure.
+ * @sproc: Pointer to the scan callback.
+ * @priv: Private opaque data passed to the @sproc callback.
+ *
+ * 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 error, pwake = 0;
+        unsigned long flags;
+        struct epitem *epi, *nepi;
+        struct list_head txlist;
+
+        INIT_LIST_HEAD(&txlist);
+
+        /*
+         * We need to lock this because we could be hit by
+         * eventpoll_release_file() and epoll_ctl(EPOLL_CTL_DEL).
+         */
+        mutex_lock(&ep->mtx);
+
+        /*
+         * Steal the ready list, and re-init the original one to the
+         * empty list. Also, set ep->ovflist to NULL so that events
+         * happening while looping w/out locks, are not lost. We cannot
+         * have the poll callback to queue directly on ep->rdllist,
+         * because we want the "sproc" callback to be able to do it
+         * in a lockless way.
+         */
+        spin_lock_irqsave(&ep->lock, flags);
+        list_splice(&ep->rdllist, &txlist);
+        INIT_LIST_HEAD(&ep->rdllist);
+        ep->ovflist = NULL;
+        spin_unlock_irqrestore(&ep->lock, flags);
+
+        /*
+         * Now call the callback function.
+         */
+        error = (*sproc)(ep, &txlist, priv);
+
+        spin_lock_irqsave(&ep->lock, flags);
+        /*
+         * During the time we spent inside the "sproc" callback, some
+         * other events might have been queued by the poll callback.
+         * We re-insert them inside the main ready-list here.
+         */
+        for (nepi = ep->ovflist; (epi = nepi) != NULL;
+             nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
+                /*
+                 * We need to check if the item is already in the list.
+                 * During the "sproc" callback execution time, items are
+                 * queued into ->ovflist but the "txlist" might already
+                 * contain them, and the list_splice() below takes care of them.
+                 */
+                if (!ep_is_linked(&epi->rdllink))
+                        list_add_tail(&epi->rdllink, &ep->rdllist);
+        }
+        /*
+         * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
+         * releasing the lock, events will be queued in the normal way inside
+         * ep->rdllist.
+         */
+        ep->ovflist = EP_UNACTIVE_PTR;
+
+        /*
+         * Quickly re-inject items left on "txlist".
+         */
+        list_splice(&txlist, &ep->rdllist);
+
+        if (!list_empty(&ep->rdllist)) {
+                /*
+                 * Wake up (if active) both the eventpoll wait list and the ->poll()
+                 * wait list (delayed after we release the lock).
+                 */
+                if (waitqueue_active(&ep->wq))
+                        wake_up_locked(&ep->wq);
+                if (waitqueue_active(&ep->poll_wait))
+                        pwake++;
+        }
+        spin_unlock_irqrestore(&ep->lock, flags);
+
+        mutex_unlock(&ep->mtx);
+
+        /* We have to call this outside the lock */
+        if (pwake)
+                ep_poll_safewake(&ep->poll_wait);
+
+        return error;
+}
+
 /*
  * Removes a "struct epitem" from the eventpoll RB tree and deallocates
  * all the associated resources. Must be called with "mtx" held.
@@ -447,7 +583,7 @@ static void ep_free(struct eventpoll *ep)
 
         /* We need to release all tasks waiting for these file */
         if (waitqueue_active(&ep->poll_wait))
-                ep_poll_safewake(&psw, &ep->poll_wait);
+                ep_poll_safewake(&ep->poll_wait);
 
         /*
          * We need to lock this because we could be hit by
@@ -496,22 +632,49 @@ static int ep_eventpoll_release(struct inode *inode, struct file *file)
         return 0;
 }
 
+static int ep_read_events_proc(struct eventpoll *ep, struct list_head *head, void *priv)
+{
+        struct epitem *epi, *tmp;
+
+        list_for_each_entry_safe(epi, tmp, head, rdllink) {
+                if (epi->ffd.file->f_op->poll(epi->ffd.file, NULL) &
+                    epi->event.events)
+                        return POLLIN | POLLRDNORM;
+                else
+                        /*
+                         * Item has been dropped into the ready list by the poll
+                         * callback, but it's not actually ready, as far as
+                         * caller requested events goes. We can remove it here.
+                         */
+                        list_del_init(&epi->rdllink);
+        }
+
+        return 0;
+}
+
+static int ep_poll_readyevents_proc(void *priv, void *cookie, int call_nests)
+{
+        return ep_scan_ready_list(priv, ep_read_events_proc, NULL);
+}
+
 static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait)
 {
-        unsigned int pollflags = 0;
-        unsigned long flags;
+        int pollflags;
         struct eventpoll *ep = file->private_data;
 
         /* Insert inside our poll wait queue */
         poll_wait(file, &ep->poll_wait, wait);
 
-        /* Check our condition */
-        spin_lock_irqsave(&ep->lock, flags);
-        if (!list_empty(&ep->rdllist))
-                pollflags = POLLIN | POLLRDNORM;
-        spin_unlock_irqrestore(&ep->lock, flags);
+        /*
+         * Proceed to find out if wanted events are really available inside
+         * the ready list. This need to be done under ep_call_nested()
+         * supervision, since the call to f_op->poll() done on listed files
+         * could re-enter here.
+         */
+        pollflags = ep_call_nested(&poll_readywalk_ncalls, EP_MAX_NESTS,
+                                   ep_poll_readyevents_proc, ep, ep);
 
-        return pollflags;
+        return pollflags != -1 ? pollflags: 0;
 }
 
 /* File callbacks that implement the eventpoll file behaviour */
@@ -541,7 +704,7 @@ void eventpoll_release_file(struct file *file)
          * We don't want to get "file->f_lock" because it is not
          * necessary. It is not necessary because we're in the "struct file"
          * cleanup path, and this means that noone is using this file anymore.
-         * So, for example, epoll_ctl() cannot hit here sicne if we reach this
+         * So, for example, epoll_ctl() cannot hit here since if we reach this
          * point, the file counter already went to zero and fget() would fail.
          * The only hit might come from ep_free() but by holding the mutex
          * will correctly serialize the operation. We do need to acquire
@@ -670,12 +833,9 @@ static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *k
         }
 
         /* If this file is already in the ready list we exit soon */
-        if (ep_is_linked(&epi->rdllink))
-                goto is_linked;
-
-        list_add_tail(&epi->rdllink, &ep->rdllist);
+        if (!ep_is_linked(&epi->rdllink))
+                list_add_tail(&epi->rdllink, &ep->rdllist);
 
-is_linked:
         /*
          * Wake up ( if active ) both the eventpoll wait list and the ->poll()
          * wait list.
@@ -690,7 +850,7 @@ out_unlock:
 
         /* We have to call this outside the lock */
         if (pwake)
-                ep_poll_safewake(&psw, &ep->poll_wait);
+                ep_poll_safewake(&ep->poll_wait);
 
         return 1;
 }
@@ -712,10 +872,9 @@ static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
                 add_wait_queue(whead, &pwq->wait);
                 list_add_tail(&pwq->llink, &epi->pwqlist);
                 epi->nwait++;
-        } else {
+        } else
                 /* We have to signal that an error occurred */
                 epi->nwait = -1;
-        }
 }
 
 static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
@@ -817,7 +976,7 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
 
         /* We have to call this outside the lock */
         if (pwake)
-                ep_poll_safewake(&psw, &ep->poll_wait);
+                ep_poll_safewake(&ep->poll_wait);
 
         DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_insert(%p, %p, %d)\n",
                      current, ep, tfile, fd));
@@ -891,137 +1050,74 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even
 
         /* We have to call this outside the lock */
         if (pwake)
-                ep_poll_safewake(&psw, &ep->poll_wait);
+                ep_poll_safewake(&ep->poll_wait);
 
         return 0;
 }
 
-static int ep_send_events(struct eventpoll *ep, struct epoll_event __user *events,
-                          int maxevents)
+static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head, void *priv)
 {
-        int eventcnt, error = -EFAULT, pwake = 0;
-        unsigned int revents;
-        unsigned long flags;
-        struct epitem *epi, *nepi;
-        struct list_head txlist;
-
-        INIT_LIST_HEAD(&txlist);
-
-        /*
-         * We need to lock this because we could be hit by
-         * eventpoll_release_file() and epoll_ctl(EPOLL_CTL_DEL).
-         */
-        mutex_lock(&ep->mtx);
-
-        /*
-         * Steal the ready list, and re-init the original one to the
-         * empty list. Also, set ep->ovflist to NULL so that events
-         * happening while looping w/out locks, are not lost. We cannot
-         * have the poll callback to queue directly on ep->rdllist,
-         * because we are doing it in the loop below, in a lockless way.
-         */
-        spin_lock_irqsave(&ep->lock, flags);
-        list_splice(&ep->rdllist, &txlist);
-        INIT_LIST_HEAD(&ep->rdllist);
-        ep->ovflist = NULL;
-        spin_unlock_irqrestore(&ep->lock, flags);
+        struct ep_send_events_data *esed = priv;
+        int eventcnt;
+        unsigned int revents;
+        struct epitem *epi;
+        struct epoll_event __user *uevent;
 
-        /*
-         * We can loop without lock because this is a task private list.
-         * We just splice'd out the ep->rdllist in ep_collect_ready_items().
-         * Items cannot vanish during the loop because we are holding "mtx".
-         */
-        for (eventcnt = 0; !list_empty(&txlist) && eventcnt < maxevents;) {
-                epi = list_first_entry(&txlist, struct epitem, rdllink);
+        /*
+         * We can loop without lock because we are passed a task private list.
+         * Items cannot vanish during the loop because ep_scan_ready_list() is
+         * holding "mtx" during this call.
+         */
+        for (eventcnt = 0, uevent = esed->events;
+             !list_empty(head) && eventcnt < esed->maxevents;) {
+                epi = list_first_entry(head, struct epitem, rdllink);
 
                 list_del_init(&epi->rdllink);
 
-                /*
-                 * Get the ready file event set. We can safely use the file
-                 * because we are holding the "mtx" and this will guarantee
-                 * that both the file and the item will not vanish.
-                 */
-                revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);
-                revents &= epi->event.events;
-
-                /*
-                 * Is the event mask intersect the caller-requested one,
-                 * deliver the event to userspace. Again, we are holding
-                 * "mtx", so no operations coming from userspace can change
-                 * the item.
-                 */
-                if (revents) {
-                        if (__put_user(revents,
-                                       &events[eventcnt].events) ||
-                            __put_user(epi->event.data,
-                                       &events[eventcnt].data))
-                                goto errxit;
-                        if (epi->event.events & EPOLLONESHOT)
-                                epi->event.events &= EP_PRIVATE_BITS;
-                        eventcnt++;
-                }
-                /*
-                 * At this point, noone can insert into ep->rdllist besides
-                 * us. The epoll_ctl() callers are locked out by us holding
-                 * "mtx" and the poll callback will queue them in ep->ovflist.
-                 */
-                if (!(epi->event.events & EPOLLET) &&
-                    (revents & epi->event.events))
-                        list_add_tail(&epi->rdllink, &ep->rdllist);
-        }
-        error = 0;
-
-errxit:
-
-        spin_lock_irqsave(&ep->lock, flags);
-        /*
-         * During the time we spent in the loop above, some other events
-         * might have been queued by the poll callback. We re-insert them
-         * inside the main ready-list here.
-         */
-        for (nepi = ep->ovflist; (epi = nepi) != NULL;
-             nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
-                /*
-                 * If the above loop quit with errors, the epoll item might still
-                 * be linked to "txlist", and the list_splice() done below will
-                 * take care of those cases.
-                 */
-                if (!ep_is_linked(&epi->rdllink))
-                        list_add_tail(&epi->rdllink, &ep->rdllist);
-        }
-        /*
-         * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
-         * releasing the lock, events will be queued in the normal way inside
-         * ep->rdllist.
-         */
-        ep->ovflist = EP_UNACTIVE_PTR;
-
-        /*
-         * In case of error in the event-send loop, or in case the number of
-         * ready events exceeds the userspace limit, we need to splice the
-         * "txlist" back inside ep->rdllist.
-         */
-        list_splice(&txlist, &ep->rdllist);
-
-        if (!list_empty(&ep->rdllist)) {
-                /*
-                 * Wake up (if active) both the eventpoll wait list and the ->poll()
-                 * wait list (delayed after we release the lock).
-                 */
-                if (waitqueue_active(&ep->wq))
-                        wake_up_locked(&ep->wq);
-                if (waitqueue_active(&ep->poll_wait))
-                        pwake++;
-        }
-        spin_unlock_irqrestore(&ep->lock, flags);
+                revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL) &
+                        epi->event.events;
+
+                /*
+                 * If the event mask intersect the caller-requested one,
+                 * deliver the event to userspace. Again, ep_scan_ready_list()
+                 * is holding "mtx", so no operations coming from userspace
+                 * can change the item.
+                 */
+                if (revents) {
+                        if (__put_user(revents, &uevent->events) ||
+                            __put_user(epi->event.data, &uevent->data))
+                                return eventcnt ? eventcnt: -EFAULT;
+                        eventcnt++;
+                        uevent++;
+                        if (epi->event.events & EPOLLONESHOT)
+                                epi->event.events &= EP_PRIVATE_BITS;
+                        else if (!(epi->event.events & EPOLLET))
+                                /*
+                                 * If this file has been added with Level Trigger
+                                 * mode, we need to insert back inside the ready
+                                 * list, so that the next call to epoll_wait()
+                                 * will check again the events availability.
+                                 * At this point, noone can insert into ep->rdllist
+                                 * besides us. The epoll_ctl() callers are locked
+                                 * out by ep_scan_ready_list() holding "mtx" and
+                                 * the poll callback will queue them in ep->ovflist.
+                                 */
+                                list_add_tail(&epi->rdllink, &ep->rdllist);
+                }
+        }
+
+        return eventcnt;
+}
 
-        mutex_unlock(&ep->mtx);
+static int ep_send_events(struct eventpoll *ep, struct epoll_event __user *events,
+                          int maxevents)
+{
+        struct ep_send_events_data esed;
 
-        /* We have to call this outside the lock */
-        if (pwake)
-                ep_poll_safewake(&psw, &ep->poll_wait);
+        esed.maxevents = maxevents;
+        esed.events = events;
 
-        return eventcnt == 0 ? error: eventcnt;
+        return ep_scan_ready_list(ep, ep_send_events_proc, &esed);
 }
 
 static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
@@ -1033,7 +1129,7 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
         wait_queue_t wait;
 
         /*
-         * Calculate the timeout by checking for the "infinite" value ( -1 )
+         * Calculate the timeout by checking for the "infinite" value (-1)
          * and the overflow condition. The passed timeout is in milliseconds,
          * that why (t * HZ) / 1000.
          */
@@ -1076,9 +1172,8 @@ retry:
 
                 set_current_state(TASK_RUNNING);
         }
-
         /* Is it worth to try to dig for events ? */
-        eavail = !list_empty(&ep->rdllist);
+        eavail = !list_empty(&ep->rdllist) || ep->ovflist != EP_UNACTIVE_PTR;
 
         spin_unlock_irqrestore(&ep->lock, flags);
 
@@ -1099,41 +1194,40 @@ retry:
  */
 SYSCALL_DEFINE1(epoll_create1, int, flags)
 {
-        int error, fd = -1;
-        struct eventpoll *ep;
+        int error;
+        struct eventpoll *ep = NULL;
 
         /* Check the EPOLL_* constant for consistency.  */
         BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC);
 
-        if (flags & ~EPOLL_CLOEXEC)
-                return -EINVAL;
-
         DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d)\n",
                      current, flags));
 
+        error = -EINVAL;
+        if (flags & ~EPOLL_CLOEXEC)
+                goto error_return;
+
         /*
-         * Create the internal data structure ( "struct eventpoll" ).
+         * Create the internal data structure ("struct eventpoll").
          */
         error = ep_alloc(&ep);
-        if (error < 0) {
-                fd = error;
+        if (error < 0)
                 goto error_return;
-        }
 
         /*
          * Creates all the items needed to setup an eventpoll file. That is,
          * a file structure and a free file descriptor.
          */
-        fd = anon_inode_getfd("[eventpoll]", &eventpoll_fops, ep,
-                              flags & O_CLOEXEC);
-        if (fd < 0)
+        error = anon_inode_getfd("[eventpoll]", &eventpoll_fops, ep,
+                                 flags & O_CLOEXEC);
+        if (error < 0)
                 ep_free(ep);
 
 error_return:
         DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d) = %d\n",
-                     current, flags, fd));
+                     current, flags, error));
 
-        return fd;
+        return error;
 }
 
 SYSCALL_DEFINE1(epoll_create, int, size)
@@ -1359,7 +1453,10 @@ static int __init eventpoll_init(void)
                 EP_ITEM_COST;
 
         /* Initialize the structure used to perform safe poll wait head wake ups */
-        ep_poll_safewake_init(&psw);
+        ep_nested_calls_init(&poll_safewake_ncalls);
+
+        /* Initialize the structure used to perform file's f_op->poll() calls */
+        ep_nested_calls_init(&poll_readywalk_ncalls);
 
         /* Allocates slab cache used to allocate "struct epitem" items */
         epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),