/* * fs/eventpoll.c (Efficent event polling implementation) * Copyright (C) 2001,...,2007 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. * * Davide Libenzi * */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include /* * LOCKING: * There are three level of locking required by epoll : * * 1) epmutex (mutex) * 2) ep->mtx (mutex) * 3) ep->lock (spinlock) * * The acquire order is the one listed above, from 1 to 3. * We need a spinlock (ep->lock) because we manipulate objects * from inside the poll callback, that might be triggered from * a wake_up() that in turn might be called from IRQ context. * So we can't sleep inside the poll callback and hence we need * a spinlock. During the event transfer loop (from kernel to * user space) we could end up sleeping due a copy_to_user(), so * we need a lock that will allow us to sleep. This lock is a * mutex (ep->mtx). It is acquired during the event transfer loop, * during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file(). * Then we also need a global mutex to serialize eventpoll_release_file() * and ep_free(). * This mutex is acquired by ep_free() during the epoll file * cleanup path and it is also acquired by eventpoll_release_file() * if a file has been pushed inside an epoll set and it is then * close()d without a previous call toepoll_ctl(EPOLL_CTL_DEL). * It is possible to drop the "ep->mtx" and to use the global * mutex "epmutex" (together with "ep->lock") to have it working, * but having "ep->mtx" will make the interface more scalable. * Events that require holding "epmutex" are very rare, while for * normal operations the epoll private "ep->mtx" will guarantee * a better scalability. */ #define DEBUG_EPOLL 0 #if DEBUG_EPOLL > 0 #define DPRINTK(x) printk x #define DNPRINTK(n, x) do { if ((n) <= DEBUG_EPOLL) printk x; } while (0) #else /* #if DEBUG_EPOLL > 0 */ #define DPRINTK(x) (void) 0 #define DNPRINTK(n, x) (void) 0 #endif /* #if DEBUG_EPOLL > 0 */ #define DEBUG_EPI 0 #if DEBUG_EPI != 0 #define EPI_SLAB_DEBUG (SLAB_DEBUG_FREE | SLAB_RED_ZONE /* | SLAB_POISON */) #else /* #if DEBUG_EPI != 0 */ #define EPI_SLAB_DEBUG 0 #endif /* #if DEBUG_EPI != 0 */ /* 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 msec timeout value storeable in a long int */ #define EP_MAX_MSTIMEO min(1000ULL * MAX_SCHEDULE_TIMEOUT / HZ, (LONG_MAX - 999ULL) / HZ) #define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event)) #define EP_UNACTIVE_PTR ((void *) -1L) struct epoll_filefd { struct file *file; int fd; }; /* * 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. */ struct wake_task_node { struct list_head llink; struct task_struct *task; wait_queue_head_t *wq; }; /* * This is used to implement the safe poll wake up avoiding to reenter * the poll callback from inside wake_up(). */ struct poll_safewake { struct list_head wake_task_list; spinlock_t lock; }; /* * Each file descriptor added to the eventpoll interface will * have an entry of this type linked to the "rbr" RB tree. */ struct epitem { /* RB tree node used to link this structure to the eventpoll RB tree */ struct rb_node rbn; /* List header used to link this structure to the eventpoll ready list */ struct list_head rdllink; /* * Works together "struct eventpoll"->ovflist in keeping the * single linked chain of items. */ struct epitem *next; /* The file descriptor information this item refers to */ struct epoll_filefd ffd; /* Number of active wait queue attached to poll operations */ int nwait; /* List containing poll wait queues */ struct list_head pwqlist; /* The "container" of this item */ struct eventpoll *ep; /* List header used to link this item to the "struct file" items list */ struct list_head fllink; /* The structure that describe the interested events and the source fd */ struct epoll_event event; }; /* * This structure is stored inside the "private_data" member of the file * structure and rapresent the main data sructure for the eventpoll * interface. */ struct eventpoll { /* Protect the this structure access */ spinlock_t lock; /* * This mutex is used to ensure that files are not removed * while epoll is using them. This is held during the event * collection loop, the file cleanup path, the epoll file exit * code and the ctl operations. */ struct mutex mtx; /* Wait queue used by sys_epoll_wait() */ wait_queue_head_t wq; /* Wait queue used by file->poll() */ wait_queue_head_t poll_wait; /* List of ready file descriptors */ struct list_head rdllist; /* RB tree root used to store monitored fd structs */ struct rb_root rbr; /* * This is a single linked list that chains all the "struct epitem" that * happened while transfering ready events to userspace w/out * holding ->lock. */ struct epitem *ovflist; }; /* Wait structure used by the poll hooks */ struct eppoll_entry { /* List header used to link this structure to the "struct epitem" */ struct list_head llink; /* The "base" pointer is set to the container "struct epitem" */ void *base; /* * Wait queue item that will be linked to the target file wait * queue head. */ wait_queue_t wait; /* The wait queue head that linked the "wait" wait queue item */ wait_queue_head_t *whead; }; /* Wrapper struct used by poll queueing */ struct ep_pqueue { poll_table pt; struct epitem *epi; }; /* * This mutex is used to serialize ep_free() and eventpoll_release_file(). */ static struct mutex epmutex; /* Safe wake up implementation */ static struct poll_safewake psw; /* Slab cache used to allocate "struct epitem" */ static struct kmem_cache *epi_cache __read_mostly; /* Slab cache used to allocate "struct eppoll_entry" */ static struct kmem_cache *pwq_cache __read_mostly; /* Setup the structure that is used as key for the RB tree */ static inline void ep_set_ffd(struct epoll_filefd *ffd, struct file *file, int fd) { ffd->file = file; ffd->fd = fd; } /* Compare RB tree keys */ static inline int ep_cmp_ffd(struct epoll_filefd *p1, struct epoll_filefd *p2) { return (p1->file > p2->file ? +1: (p1->file < p2->file ? -1 : p1->fd - p2->fd)); } /* Tells us if the item is currently linked */ static inline int ep_is_linked(struct list_head *p) { return !list_empty(p); } /* Get the "struct epitem" from a wait queue pointer */ static inline struct epitem *ep_item_from_wait(wait_queue_t *p) { return container_of(p, struct eppoll_entry, wait)->base; } /* Get the "struct epitem" from an epoll queue wrapper */ static inline struct epitem *ep_item_from_epqueue(poll_table *p) { return container_of(p, struct ep_pqueue, pt)->epi; } /* Tells if the epoll_ctl(2) operation needs an event copy from userspace */ static inline int ep_op_has_event(int op) { return op != EPOLL_CTL_DEL; } /* Initialize the poll safe wake up structure */ static void ep_poll_safewake_init(struct poll_safewake *psw) { INIT_LIST_HEAD(&psw->wake_task_list); spin_lock_init(&psw->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. */ static void ep_poll_safewake(struct poll_safewake *psw, wait_queue_head_t *wq) { int wake_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; spin_lock_irqsave(&psw->lock, flags); /* Try to see if the current task is already inside this wakeup call */ list_for_each_entry(tncur, lsthead, llink) { if (tncur->wq == wq || (tncur->task == this_task && ++wake_nests > EP_MAX_POLLWAKE_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; } } /* Add the current task to the list */ tnode.task = this_task; tnode.wq = wq; list_add(&tnode.llink, lsthead); spin_unlock_irqrestore(&psw->lock, flags); /* Do really wake up now */ wake_up_nested(wq, 1 + wake_nests); /* Remove the current task from the list */ spin_lock_irqsave(&psw->lock, flags); list_del(&tnode.llink); spin_unlock_irqrestore(&psw->lock, flags); } /* * This function unregister poll callbacks from the associated file descriptor. * Since this must be called without holding "ep->lock" the atomic exchange trick * will protect us from multiple unregister. */ static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi) { int nwait; struct list_head *lsthead = &epi->pwqlist; struct eppoll_entry *pwq; /* This is called without locks, so we need the atomic exchange */ nwait = xchg(&epi->nwait, 0); if (nwait) { while (!list_empty(lsthead)) { pwq = list_first_entry(lsthead, struct eppoll_entry, llink); list_del_init(&pwq->llink); remove_wait_queue(pwq->whead, &pwq->wait); kmem_cache_free(pwq_cache, pwq); } } } /* * Removes a "struct epitem" from the eventpoll RB tree and deallocates * all the associated resources. Must be called with "mtx" held. */ static int ep_remove(struct eventpoll *ep, struct epitem *epi) { unsigned long flags; struct file *file = epi->ffd.file; /* * Removes poll wait queue hooks. We _have_ to do this without holding * the "ep->lock" otherwise a deadlock might occur. This because of the * sequence of the lock acquisition. Here we do "ep->lock" then the wait * queue head lock when unregistering the wait queue. The wakeup callback * will run by holding the wait queue head lock and will call our callback * that will try to get "ep->lock". */ ep_unregister_pollwait(ep, epi); /* Remove the current item from the list of epoll hooks */ spin_lock(&file->f_ep_lock); if (ep_is_linked(&epi->fllink)) list_del_init(&epi->fllink); spin_unlock(&file->f_ep_lock); rb_erase(&epi->rbn, &ep->rbr); spin_lock_irqsave(&ep->lock, flags); if (ep_is_linked(&epi->rdllink)) list_del_init(&epi->rdllink); spin_unlock_irqrestore(&ep->lock, flags); /* At this point it is safe to free the eventpoll item */ kmem_cache_free(epi_cache, epi); DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_remove(%p, %p)\n", current, ep, file)); return 0; } static void ep_free(struct eventpoll *ep) { struct rb_node *rbp; struct epitem *epi; /* We need to release all tasks waiting for these file */ if (waitqueue_active(&ep->poll_wait)) ep_poll_safewake(&psw, &ep->poll_wait); /* * We need to lock this because we could be hit by * eventpoll_release_file() while we're freeing the "struct eventpoll". * We do not need to hold "ep->mtx" here because the epoll file * is on the way to be removed and no one has references to it * anymore. The only hit might come from eventpoll_release_file() but * holding "epmutex" is sufficent here. */ mutex_lock(&epmutex); /* * Walks through the whole tree by unregistering poll callbacks. */ for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) { epi = rb_entry(rbp, struct epitem, rbn); ep_unregister_pollwait(ep, epi); } /* * Walks through the whole tree by freeing each "struct epitem". At this * point we are sure no poll callbacks will be lingering around, and also by * holding "epmutex" we can be sure that no file cleanup code will hit * us during this operation. So we can avoid the lock on "ep->lock". */ while ((rbp = rb_first(&ep->rbr)) != NULL) { epi = rb_entry(rbp, struct epitem, rbn); ep_remove(ep, epi); } mutex_unlock(&epmutex); mutex_destroy(&ep->mtx); kfree(ep); } static int ep_eventpoll_release(struct inode *inode, struct file *file) { struct eventpoll *ep = file->private_data; if (ep) ep_free(ep); DNPRINTK(3, (KERN_INFO "[%p] eventpoll: close() ep=%p\n", current, ep)); return 0; } static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait) { unsigned int pollflags = 0; unsigned long flags; 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); return pollflags; } /* File callbacks that implement the eventpoll file behaviour */ static const struct file_operations eventpoll_fops = { .release = ep_eventpoll_release, .poll = ep_eventpoll_poll }; /* Fast test to see if the file is an evenpoll file */ static inline int is_file_epoll(struct file *f) { return f->f_op == &eventpoll_fops; } /* * This is called from eventpoll_release() to unlink files from the eventpoll * interface. We need to have this facility to cleanup correctly files that are * closed without being removed from the eventpoll interface. */ void eventpoll_release_file(struct file *file) { struct list_head *lsthead = &file->f_ep_links; struct eventpoll *ep; struct epitem *epi; /* * We don't want to get "file->f_ep_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 * 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 * "ep->mtx" after "epmutex" because ep_remove() requires it when called * from anywhere but ep_free(). */ mutex_lock(&epmutex); while (!list_empty(lsthead)) { epi = list_first_entry(lsthead, struct epitem, fllink); ep = epi->ep; list_del_init(&epi->fllink); mutex_lock(&ep->mtx); ep_remove(ep, epi); mutex_unlock(&ep->mtx); } mutex_unlock(&epmutex); } static int ep_alloc(struct eventpoll **pep) { struct eventpoll *ep = kzalloc(sizeof(*ep), GFP_KERNEL); if (!ep) return -ENOMEM; spin_lock_init(&ep->lock); mutex_init(&ep->mtx); init_waitqueue_head(&ep->wq); init_waitqueue_head(&ep->poll_wait); INIT_LIST_HEAD(&ep->rdllist); ep->rbr = RB_ROOT; ep->ovflist = EP_UNACTIVE_PTR; *pep = ep; DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_alloc() ep=%p\n", current, ep)); return 0; } /* * Search the file inside the eventpoll tree. The RB tree operations * are protected by the "mtx" mutex, and ep_find() must be called with * "mtx" held. */ static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd) { int kcmp; struct rb_node *rbp; struct epitem *epi, *epir = NULL; struct epoll_filefd ffd; ep_set_ffd(&ffd, file, fd); for (rbp = ep->rbr.rb_node; rbp; ) { epi = rb_entry(rbp, struct epitem, rbn); kcmp = ep_cmp_ffd(&ffd, &epi->ffd); if (kcmp > 0) rbp = rbp->rb_right; else if (kcmp < 0) rbp = rbp->rb_left; else { epir = epi; break; } } DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_find(%p) -> %p\n", current, file, epir)); return epir; } /* * This is the callback that is passed to the wait queue wakeup * machanism. It is called by the stored file descriptors when they * have events to report. */ static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *key) { int pwake = 0; unsigned long flags; struct epitem *epi = ep_item_from_wait(wait); struct eventpoll *ep = epi->ep; DNPRINTK(3, (KERN_INFO "[%p] eventpoll: poll_callback(%p) epi=%p ep=%p\n", current, epi->ffd.file, epi, ep)); spin_lock_irqsave(&ep->lock, flags); /* * If the event mask does not contain any poll(2) event, we consider the * descriptor to be disabled. This condition is likely the effect of the * EPOLLONESHOT bit that disables the descriptor when an event is received, * until the next EPOLL_CTL_MOD will be issued. */ if (!(epi->event.events & ~EP_PRIVATE_BITS)) goto out_unlock; /* * If we are trasfering events to userspace, we can hold no locks * (because we're accessing user memory, and because of linux f_op->poll() * semantics). All the events that happens during that period of time are * chained in ep->ovflist and requeued later on. */ if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) { if (epi->next == EP_UNACTIVE_PTR) { epi->next = ep->ovflist; ep->ovflist = epi; } goto out_unlock; } /* 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); is_linked: /* * Wake up ( if active ) both the eventpoll wait list and the ->poll() * wait list. */ if (waitqueue_active(&ep->wq)) wake_up_locked(&ep->wq); if (waitqueue_active(&ep->poll_wait)) pwake++; out_unlock: spin_unlock_irqrestore(&ep->lock, flags); /* We have to call this outside the lock */ if (pwake) ep_poll_safewake(&psw, &ep->poll_wait); return 1; } /* * This is the callback that is used to add our wait queue to the * target file wakeup lists. */ static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, poll_table *pt) { struct epitem *epi = ep_item_from_epqueue(pt); struct eppoll_entry *pwq; if (epi->nwait >= 0 && (pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL))) { init_waitqueue_func_entry(&pwq->wait, ep_poll_callback); pwq->whead = whead; pwq->base = epi; add_wait_queue(whead, &pwq->wait); list_add_tail(&pwq->llink, &epi->pwqlist); epi->nwait++; } else { /* We have to signal that an error occurred */ epi->nwait = -1; } } static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi) { int kcmp; struct rb_node **p = &ep->rbr.rb_node, *parent = NULL; struct epitem *epic; while (*p) { parent = *p; epic = rb_entry(parent, struct epitem, rbn); kcmp = ep_cmp_ffd(&epi->ffd, &epic->ffd); if (kcmp > 0) p = &parent->rb_right; else p = &parent->rb_left; } rb_link_node(&epi->rbn, parent, p); rb_insert_color(&epi->rbn, &ep->rbr); } /* * Must be called with "mtx" held. */ static int ep_insert(struct eventpoll *ep, struct epoll_event *event, struct file *tfile, int fd) { int error, revents, pwake = 0; unsigned long flags; struct epitem *epi; struct ep_pqueue epq; error = -ENOMEM; if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL))) goto error_return; /* Item initialization follow here ... */ INIT_LIST_HEAD(&epi->rdllink); INIT_LIST_HEAD(&epi->fllink); INIT_LIST_HEAD(&epi->pwqlist); epi->ep = ep; ep_set_ffd(&epi->ffd, tfile, fd); epi->event = *event; epi->nwait = 0; epi->next = EP_UNACTIVE_PTR; /* Initialize the poll table using the queue callback */ epq.epi = epi; init_poll_funcptr(&epq.pt, ep_ptable_queue_proc); /* * Attach the item to the poll hooks and get current event bits. * We can safely use the file* here because its usage count has * been increased by the caller of this function. Note that after * this operation completes, the poll callback can start hitting * the new item. */ revents = tfile->f_op->poll(tfile, &epq.pt); /* * We have to check if something went wrong during the poll wait queue * install process. Namely an allocation for a wait queue failed due * high memory pressure. */ if (epi->nwait < 0) goto error_unregister; /* Add the current item to the list of active epoll hook for this file */ spin_lock(&tfile->f_ep_lock); list_add_tail(&epi->fllink, &tfile->f_ep_links); spin_unlock(&tfile->f_ep_lock); /* * Add the current item to the RB tree. All RB tree operations are * protected by "mtx", and ep_insert() is called with "mtx" held. */ ep_rbtree_insert(ep, epi); /* We have to drop the new item inside our item list to keep track of it */ spin_lock_irqsave(&ep->lock, flags); /* If the file is already "ready" we drop it inside the ready list */ if ((revents & event->events) && !ep_is_linked(&epi->rdllink)) { list_add_tail(&epi->rdllink, &ep->rdllist); /* Notify waiting tasks that events are available */ if (waitqueue_active(&ep->wq)) wake_up_locked(&ep->wq); if (waitqueue_active(&ep->poll_wait)) pwake++; } spin_unlock_irqrestore(&ep->lock, flags); /* We have to call this outside the lock */ if (pwake) ep_poll_safewake(&psw, &ep->poll_wait); DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_insert(%p, %p, %d)\n", current, ep, tfile, fd)); return 0; error_unregister: ep_unregister_pollwait(ep, epi); /* * We need to do this because an event could have been arrived on some * allocated wait queue. Note that we don't care about the ep->ovflist * list, since that is used/cleaned only inside a section bound by "mtx". * And ep_insert() is called with "mtx" held. */ spin_lock_irqsave(&ep->lock, flags); if (ep_is_linked(&epi->rdllink)) list_del_init(&epi->rdllink); spin_unlock_irqrestore(&ep->lock, flags); kmem_cache_free(epi_cache, epi); error_return: return error; } /* * Modify the interest event mask by dropping an event if the new mask * has a match in the current file status. Must be called with "mtx" held. */ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event) { int pwake = 0; unsigned int revents; unsigned long flags; /* * Set the new event interest mask before calling f_op->poll(), otherwise * a potential race might occur. In fact if we do this operation inside * the lock, an event might happen between the f_op->poll() call and the * new event set registering. */ epi->event.events = event->events; /* * 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); spin_lock_irqsave(&ep->lock, flags); /* Copy the data member from inside the lock */ epi->event.data = event->data; /* * If the item is "hot" and it is not registered inside the ready * list, push it inside. */ if (revents & event->events) { if (!ep_is_linked(&epi->rdllink)) { list_add_tail(&epi->rdllink, &ep->rdllist); /* Notify waiting tasks that events are available */ if (waitqueue_active(&ep->wq)) wake_up_locked(&ep->wq); if (waitqueue_active(&ep->poll_wait)) pwake++; } } spin_unlock_irqrestore(&ep->lock, flags); /* We have to call this outside the lock */ if (pwake) ep_poll_safewake(&psw, &ep->poll_wait); return 0; } static int ep_send_events(struct eventpoll *ep, struct epoll_event __user *events, int maxevents) { 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) 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); mutex_unlock(&ep->mtx); /* We have to call this outside the lock */ if (pwake) ep_poll_safewake(&psw, &ep->poll_wait); return eventcnt == 0 ? error: eventcnt; } static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, int maxevents, long timeout) { int res, eavail; unsigned long flags; long jtimeout; wait_queue_t wait; /* * 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. */ jtimeout = (timeout < 0 || timeout >= EP_MAX_MSTIMEO) ? MAX_SCHEDULE_TIMEOUT : (timeout * HZ + 999) / 1000; retry: spin_lock_irqsave(&ep->lock, flags); res = 0; if (list_empty(&ep->rdllist)) { /* * We don't have any available event to return to the caller. * We need to sleep here, and we will be wake up by * ep_poll_callback() when events will become available. */ init_waitqueue_entry(&wait, current); wait.flags |= WQ_FLAG_EXCLUSIVE; __add_wait_queue(&ep->wq, &wait); for (;;) { /* * We don't want to sleep if the ep_poll_callback() sends us * a wakeup in between. That's why we set the task state * to TASK_INTERRUPTIBLE before doing the checks. */ set_current_state(TASK_INTERRUPTIBLE); if (!list_empty(&ep->rdllist) || !jtimeout) break; if (signal_pending(current)) { res = -EINTR; break; } spin_unlock_irqrestore(&ep->lock, flags); jtimeout = schedule_timeout(jtimeout); spin_lock_irqsave(&ep->lock, flags); } __remove_wait_queue(&ep->wq, &wait); set_current_state(TASK_RUNNING); } /* Is it worth to try to dig for events ? */ eavail = !list_empty(&ep->rdllist); spin_unlock_irqrestore(&ep->lock, flags); /* * Try to transfer events to user space. In case we get 0 events and * there's still timeout left over, we go trying again in search of * more luck. */ if (!res && eavail && !(res = ep_send_events(ep, events, maxevents)) && jtimeout) goto retry; return res; } /* * Open an eventpoll file descriptor. */ asmlinkage long sys_epoll_create1(int flags) { int error, fd = -1; struct eventpoll *ep; /* 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)); /* * Create the internal data structure ( "struct eventpoll" ). */ error = ep_alloc(&ep); if (error < 0) { fd = error; 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) ep_free(ep); error_return: DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d) = %d\n", current, flags, fd)); return fd; } asmlinkage long sys_epoll_create(int size) { if (size < 0) return -EINVAL; return sys_epoll_create1(0); } /* * The following function implements the controller interface for * the eventpoll file that enables the insertion/removal/change of * file descriptors inside the interest set. */ asmlinkage long sys_epoll_ctl(int epfd, int op, int fd, struct epoll_event __user *event) { int error; struct file *file, *tfile; struct eventpoll *ep; struct epitem *epi; struct epoll_event epds; DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_ctl(%d, %d, %d, %p)\n", current, epfd, op, fd, event)); error = -EFAULT; if (ep_op_has_event(op) && copy_from_user(&epds, event, sizeof(struct epoll_event))) goto error_return; /* Get the "struct file *" for the eventpoll file */ error = -EBADF; file = fget(epfd); if (!file) goto error_return; /* Get the "struct file *" for the target file */ tfile = fget(fd); if (!tfile) goto error_fput; /* The target file descriptor must support poll */ error = -EPERM; if (!tfile->f_op || !tfile->f_op->poll) goto error_tgt_fput; /* * We have to check that the file structure underneath the file descriptor * the user passed to us _is_ an eventpoll file. And also we do not permit * adding an epoll file descriptor inside itself. */ error = -EINVAL; if (file == tfile || !is_file_epoll(file)) goto error_tgt_fput; /* * At this point it is safe to assume that the "private_data" contains * our own data structure. */ ep = file->private_data; mutex_lock(&ep->mtx); /* * Try to lookup the file inside our RB tree, Since we grabbed "mtx" * above, we can be sure to be able to use the item looked up by * ep_find() till we release the mutex. */ epi = ep_find(ep, tfile, fd); error = -EINVAL; switch (op) { case EPOLL_CTL_ADD: if (!epi) { epds.events |= POLLERR | POLLHUP; error = ep_insert(ep, &epds, tfile, fd); } else error = -EEXIST; break; case EPOLL_CTL_DEL: if (epi) error = ep_remove(ep, epi); else error = -ENOENT; break; case EPOLL_CTL_MOD: if (epi) { epds.events |= POLLERR | POLLHUP; error = ep_modify(ep, epi, &epds); } else error = -ENOENT; break; } mutex_unlock(&ep->mtx); error_tgt_fput: fput(tfile); error_fput: fput(file); error_return: DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_ctl(%d, %d, %d, %p) = %d\n", current, epfd, op, fd, event, error)); return error; } /* * Implement the event wait interface for the eventpoll file. It is the kernel * part of the user space epoll_wait(2). */ asmlinkage long sys_epoll_wait(int epfd, struct epoll_event __user *events, int maxevents, int timeout) { int error; struct file *file; struct eventpoll *ep; DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_wait(%d, %p, %d, %d)\n", current, epfd, events, maxevents, timeout)); /* The maximum number of event must be greater than zero */ if (maxevents <= 0 || maxevents > EP_MAX_EVENTS) return -EINVAL; /* Verify that the area passed by the user is writeable */ if (!access_ok(VERIFY_WRITE, events, maxevents * sizeof(struct epoll_event))) { error = -EFAULT; goto error_return; } /* Get the "struct file *" for the eventpoll file */ error = -EBADF; file = fget(epfd); if (!file) goto error_return; /* * We have to check that the file structure underneath the fd * the user passed to us _is_ an eventpoll file. */ error = -EINVAL; if (!is_file_epoll(file)) goto error_fput; /* * At this point it is safe to assume that the "private_data" contains * our own data structure. */ ep = file->private_data; /* Time to fish for events ... */ error = ep_poll(ep, events, maxevents, timeout); error_fput: fput(file); error_return: DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_wait(%d, %p, %d, %d) = %d\n", current, epfd, events, maxevents, timeout, error)); return error; } #ifdef HAVE_SET_RESTORE_SIGMASK /* * Implement the event wait interface for the eventpoll file. It is the kernel * part of the user space epoll_pwait(2). */ asmlinkage long sys_epoll_pwait(int epfd, struct epoll_event __user *events, int maxevents, int timeout, const sigset_t __user *sigmask, size_t sigsetsize) { int error; sigset_t ksigmask, sigsaved; /* * If the caller wants a certain signal mask to be set during the wait, * we apply it here. */ if (sigmask) { if (sigsetsize != sizeof(sigset_t)) return -EINVAL; if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask))) return -EFAULT; sigdelsetmask(&ksigmask, sigmask(SIGKILL) | sigmask(SIGSTOP)); sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved); } error = sys_epoll_wait(epfd, events, maxevents, timeout); /* * If we changed the signal mask, we need to restore the original one. * In case we've got a signal while waiting, we do not restore the * signal mask yet, and we allow do_signal() to deliver the signal on * the way back to userspace, before the signal mask is restored. */ if (sigmask) { if (error == -EINTR) { memcpy(¤t->saved_sigmask, &sigsaved, sizeof(sigsaved)); set_restore_sigmask(); } else sigprocmask(SIG_SETMASK, &sigsaved, NULL); } return error; } #endif /* HAVE_SET_RESTORE_SIGMASK */ static int __init eventpoll_init(void) { mutex_init(&epmutex); /* Initialize the structure used to perform safe poll wait head wake ups */ ep_poll_safewake_init(&psw); /* Allocates slab cache used to allocate "struct epitem" items */ epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem), 0, SLAB_HWCACHE_ALIGN|EPI_SLAB_DEBUG|SLAB_PANIC, NULL); /* Allocates slab cache used to allocate "struct eppoll_entry" */ pwq_cache = kmem_cache_create("eventpoll_pwq", sizeof(struct eppoll_entry), 0, EPI_SLAB_DEBUG|SLAB_PANIC, NULL); return 0; } fs_initcall(eventpoll_init);