/*
- * 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
/* 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)
};
/*
- * 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;
};
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/
*/
*/
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;
}
/* 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);
}
/*
}
}
+/**
+ * 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.
/* 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
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 */
* 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
}
/* 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.
/* 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;
}
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)
/* 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));
/* 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,
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.
*/
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);
*/
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)
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),
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