Re: Unexpected cascaded epoll behavior - my mistake or kernel bug

From: Davide Libenzi
Date: Sat Jan 24 2009 - 16:59:24 EST

On Fri, 23 Jan 2009, Pavel Pisa wrote:

> Hello Davide and all others,
>
> I have got to implementing yet another event library and I experience
> something strange when level triggered epoll_wait() monitors another
> level triggered epoll set. Top level epoll_wait() return information
> about one event pending. The event points correctly to the monitored
> second level epoll fd, but epoll_wait() on this fd with 0 or small timeout
> returns zero/no events and top level epoll reporting is not reset at this
> point so program enters busy loop. If there are events, they are processed
> correctly. More interresting is, that the ill behavior is prevented if I
> change number of debug writes into unrelated fd or if the application
> is slowed down by strace to standard output. The strace to the
> file does not (fortunatelly) hide ill behavior to the strange behavior
> of my code or kernel can be documented in attached straces. The both
> traces documents the busy loop cause for case, where there is created
> epoll set with fd #3, that set monitors fd #0. When character arrives
> at fd #0, the new epoll fd set with fd #4 is created ad fd #3 is added
> into this new top level fd set.
>
> epoll_create(8) = 3
> epoll_ctl(3, EPOLL_CTL_ADD, 0, {EPOLLIN, {u32=6353264, u64=6353264}}) = 0
> epoll_wait(3, {{EPOLLIN, {u32=6353264, u64=6353264}}}, 8, 20000) = 1
> read(0, "E"..., 1) = 1
> ...
> epoll_create(8) = 4
> epoll_ctl(4, EPOLL_CTL_ADD, 3, {EPOLLIN, {u32=6353664, u64=6353664}}) = 0
> epoll_wait(4, {{EPOLLIN, {u32=6353664, u64=6353664}}}, 8, 19998) = 1
> epoll_wait(3, {{EPOLLIN, {u32=6353264, u64=6353264}}}, 8, 0) = 1
> read(0, "\n"..., 1) = 1
> epoll_wait(4, {{EPOLLIN, {u32=6353664, u64=6353664}}}, 8, 19998) = 1
> epoll_wait(3, {}, 8, 0) = 0
> epoll_wait(4, {{EPOLLIN, {u32=6353664, u64=6353664}}}, 8, 19998) = 1
> epoll_wait(3, {}, 8, 0) = 0
>
> You may ask, why that terrible clam starts to writting new event library code
> and why he needs to cascade event handling mechanisms. I try to defend myself
> a little. If you do not like beat me, you can skip next section

Pavel, can you give the patch below a spin? It's working fine in my two
boxes, but it'd be great if you could confirm it too.
Attached there's also a simple test program to check epoll behavior,
especially the one related to recursion.




- Davide


---
fs/eventpoll.c | 495 ++++++++++++++++++++++++++++++++++-----------------------
1 file changed, 296 insertions(+), 199 deletions(-)

Index: linux-2.6.mod/fs/eventpoll.c
===================================================================
--- linux-2.6.mod.orig/fs/eventpoll.c 2009-01-24 10:06:52.000000000 -0800
+++ linux-2.6.mod/fs/eventpoll.c 2009-01-24 13:07:54.000000000 -0800
@@ -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 @@
};

/*
- * 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 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/
*/
@@ -244,8 +247,11 @@
*/
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;
@@ -322,64 +328,95 @@
}

/* 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 */
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);
}

/*
@@ -407,6 +444,104 @@
}
}

+/**
+ * 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.
@@ -457,7 +592,7 @@

/* 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
@@ -507,22 +642,44 @@
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
+ 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 */
@@ -703,7 +860,7 @@

/* 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;
}
@@ -830,7 +987,7 @@

/* 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));
@@ -904,137 +1061,74 @@

/* 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);
-
- /*
- * 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);
-
- 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;
+ struct ep_send_events_data *esed = priv;
+ int eventcnt;
+ unsigned int revents;
+ struct epitem *epi;
+ struct epoll_event __user *uevent;

- /*
- * 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);
+ /*
+ * 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(head);
+
+ 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);
+ }
+ }

- 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);
+ 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,
@@ -1046,7 +1140,7 @@
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.
*/
@@ -1112,42 +1206,42 @@
*/
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);
- atomic_inc(&ep->user->epoll_devs);
+ else
+ atomic_inc(&ep->user->epoll_devs);

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)
@@ -1371,7 +1465,10 @@
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),/*
* epoll_test by Davide Libenzi (Simple code to test epoll internals)
* Copyright (C) 2008 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
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
* Davide Libenzi <davidel@xxxxxxxxxxxxxxx>
*
*/

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <signal.h>
#include <limits.h>
#include <poll.h>
#include <sys/epoll.h>
#include <sys/wait.h>

#define EPWAIT_TIMEO (1 * 1000)
#ifndef POLLRDHUP
#define POLLRDHUP 0x2000
#endif

#define EPOLL_MAX_CHAIN 100L

#define EPOLL_TF_LOOP (1 << 0)

struct epoll_test_cfg {
long size;
long flags;
};

static int xepoll_create(int n) {
int epfd;

if ((epfd = epoll_create(n)) == -1) {
perror("epoll_create");
exit(2);
}

return epfd;
}

static void xepoll_ctl(int epfd, int cmd, int fd, struct epoll_event *evt) {
if (epoll_ctl(epfd, cmd, fd, evt) < 0) {
perror("epoll_ctl");
exit(3);
}
}

static void xpipe(int *fds) {
if (pipe(fds)) {
perror("pipe");
exit(4);
}
}

static pid_t xfork(void) {
pid_t pid;

if ((pid = fork()) == (pid_t) -1) {
perror("pipe");
exit(5);
}

return pid;
}

static int run_forked_proc(int (*proc)(void *), void *data) {
int status;
pid_t pid;

if ((pid = xfork()) == 0)
exit((*proc)(data));
if (waitpid(pid, &status, 0) != pid) {
perror("waitpid");
return -1;
}

return WIFEXITED(status) ? WEXITSTATUS(status): -2;
}

static int check_events(int fd, int timeo) {
struct pollfd pfd;

fprintf(stdout, "Checking events for fd %d\n", fd);
memset(&pfd, 0, sizeof(pfd));
pfd.fd = fd;
pfd.events = POLLIN | POLLOUT;
if (poll(&pfd, 1, timeo) < 0) {
perror("poll()");
return 0;
}
if (pfd.revents & POLLIN)
fprintf(stdout, "\tPOLLIN\n");
if (pfd.revents & POLLOUT)
fprintf(stdout, "\tPOLLOUT\n");
if (pfd.revents & POLLERR)
fprintf(stdout, "\tPOLLERR\n");
if (pfd.revents & POLLHUP)
fprintf(stdout, "\tPOLLHUP\n");
if (pfd.revents & POLLRDHUP)
fprintf(stdout, "\tPOLLRDHUP\n");

return pfd.revents;
}

static int epoll_test_tty(void *data) {
int epfd, ifd = fileno(stdin), res;
struct epoll_event evt;

if (check_events(ifd, 0) != POLLOUT) {
fprintf(stderr, "Something is cooking on STDIN (%d)\n", ifd);
return 1;
}
epfd = xepoll_create(1);
fprintf(stdout, "Created epoll fd (%d)\n", epfd);
memset(&evt, 0, sizeof(evt));
evt.events = EPOLLIN;
xepoll_ctl(epfd, EPOLL_CTL_ADD, ifd, &evt);
if (check_events(epfd, 0) & POLLIN) {
res = epoll_wait(epfd, &evt, 1, 0);
if (res == 0) {
fprintf(stderr, "Epoll fd (%d) is ready when it shouldn't!\n",
epfd);
return 2;
}
}

return 0;
}

static int epoll_wakeup_chain(void *data) {
struct epoll_test_cfg *tcfg = data;
int i, res, epfd, bfd, nfd, pfds[2];
pid_t pid;
struct epoll_event evt;

memset(&evt, 0, sizeof(evt));
evt.events = EPOLLIN;

epfd = bfd = xepoll_create(1);

for (i = 0; i < tcfg->size; i++) {
nfd = xepoll_create(1);
xepoll_ctl(bfd, EPOLL_CTL_ADD, nfd, &evt);
bfd = nfd;
}

if (tcfg->flags & EPOLL_TF_LOOP)
xepoll_ctl(bfd, EPOLL_CTL_ADD, epfd, &evt);

xpipe(pfds);
xepoll_ctl(bfd, EPOLL_CTL_ADD, pfds[0], &evt);

/*
* The pipe write must come after the poll(2) call inside
* check_events(). This tests the nested wakeup code in
* fs/eventpoll.c:ep_poll_safewake()
* By having the check_events() (hence poll(2)) happens first,
* we have poll wait queue filled up, and the write(2) in the
* child will trigger the wakeup chain.
*/
if ((pid = xfork()) == 0) {
sleep(1);
write(pfds[1], "w", 1);
exit(0);
}

res = check_events(epfd, 2000) & POLLIN;

if (waitpid(pid, NULL, 0) != pid) {
perror("waitpid");
return -1;
}

return res;
}

static int epoll_poll_chain(void *data) {
struct epoll_test_cfg *tcfg = data;
int i, res, epfd, bfd, nfd, pfds[2];
pid_t pid;
struct epoll_event evt;

memset(&evt, 0, sizeof(evt));
evt.events = EPOLLIN;

epfd = bfd = xepoll_create(1);

for (i = 0; i < tcfg->size; i++) {
nfd = xepoll_create(1);
xepoll_ctl(bfd, EPOLL_CTL_ADD, nfd, &evt);
bfd = nfd;
}

if (tcfg->flags & EPOLL_TF_LOOP)
xepoll_ctl(bfd, EPOLL_CTL_ADD, epfd, &evt);

xpipe(pfds);
xepoll_ctl(bfd, EPOLL_CTL_ADD, pfds[0], &evt);

/*
* The pipe write mush come before the poll(2) call inside
* check_events(). This tests the nested f_op->poll calls code in
* fs/eventpoll.c:ep_eventpoll_poll()
* By having the pipe write(2) happen first, we make the kernel
* epoll code to load the ready lists, and the following poll(2)
* done inside check_events() will test nested poll code in
* ep_eventpoll_poll().
*/
if ((pid = xfork()) == 0) {
write(pfds[1], "w", 1);
exit(0);
}
sleep(1);
res = check_events(epfd, 1000) & POLLIN;

if (waitpid(pid, NULL, 0) != pid) {
perror("waitpid");
return -1;
}

return res;
}

int main(int ac, char **av) {
int error;
struct epoll_test_cfg tcfg;

fprintf(stdout, "\n********** Testing TTY events\n");
error = run_forked_proc(epoll_test_tty, NULL);
fprintf(stdout, error == 0 ?
"********** OK\n": "********** FAIL (%d)\n", error);

tcfg.size = 3;
tcfg.flags = 0;
fprintf(stdout, "\n********** Testing short wakeup chain\n");
error = run_forked_proc(epoll_wakeup_chain, &tcfg);
fprintf(stdout, error == POLLIN ?
"********** OK\n": "********** FAIL (%d)\n", error);

tcfg.size = EPOLL_MAX_CHAIN;
tcfg.flags = 0;
fprintf(stdout, "\n********** Testing long wakeup chain (HOLD ON)\n");
error = run_forked_proc(epoll_wakeup_chain, &tcfg);
fprintf(stdout, error == 0 ?
"********** OK\n": "********** FAIL (%d)\n", error);

tcfg.size = 3;
tcfg.flags = 0;
fprintf(stdout, "\n********** Testing short poll chain\n");
error = run_forked_proc(epoll_poll_chain, &tcfg);
fprintf(stdout, error == POLLIN ?
"********** OK\n": "********** FAIL (%d)\n", error);

tcfg.size = EPOLL_MAX_CHAIN;
tcfg.flags = 0;
fprintf(stdout, "\n********** Testing long poll chain (HOLD ON)\n");
error = run_forked_proc(epoll_poll_chain, &tcfg);
fprintf(stdout, error == 0 ?
"********** OK\n": "********** FAIL (%d)\n", error);

tcfg.size = 3;
tcfg.flags = EPOLL_TF_LOOP;
fprintf(stdout, "\n********** Testing loopy wakeup chain (HOLD ON)\n");
error = run_forked_proc(epoll_wakeup_chain, &tcfg);
fprintf(stdout, error == 0 ?
"********** OK\n": "********** FAIL (%d)\n", error);

tcfg.size = 3;
tcfg.flags = EPOLL_TF_LOOP;
fprintf(stdout, "\n********** Testing loopy poll chain (HOLD ON)\n");
error = run_forked_proc(epoll_poll_chain, &tcfg);
fprintf(stdout, error == 0 ?
"********** OK\n": "********** FAIL (%d)\n", error);


return 0;
}