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Diffstat (limited to 'kernel/fs/eventpoll.c')
| -rw-r--r-- | kernel/fs/eventpoll.c | 2133 |
1 files changed, 2133 insertions, 0 deletions
diff --git a/kernel/fs/eventpoll.c b/kernel/fs/eventpoll.c new file mode 100644 index 000000000..d0c12504d --- /dev/null +++ b/kernel/fs/eventpoll.c @@ -0,0 +1,2133 @@ +/* + * 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 + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * Davide Libenzi <davidel@xmailserver.org> + * + */ + +#include <linux/init.h> +#include <linux/kernel.h> +#include <linux/sched.h> +#include <linux/fs.h> +#include <linux/file.h> +#include <linux/signal.h> +#include <linux/errno.h> +#include <linux/mm.h> +#include <linux/slab.h> +#include <linux/poll.h> +#include <linux/string.h> +#include <linux/list.h> +#include <linux/hash.h> +#include <linux/spinlock.h> +#include <linux/syscalls.h> +#include <linux/rbtree.h> +#include <linux/wait.h> +#include <linux/eventpoll.h> +#include <linux/mount.h> +#include <linux/bitops.h> +#include <linux/mutex.h> +#include <linux/anon_inodes.h> +#include <linux/device.h> +#include <asm/uaccess.h> +#include <asm/io.h> +#include <asm/mman.h> +#include <linux/atomic.h> +#include <linux/proc_fs.h> +#include <linux/seq_file.h> +#include <linux/compat.h> +#include <linux/rculist.h> + +/* + * 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 to epoll_ctl(EPOLL_CTL_DEL). + * It is also acquired when inserting an epoll fd onto another epoll + * fd. We do this so that we walk the epoll tree and ensure that this + * insertion does not create a cycle of epoll file descriptors, which + * could lead to deadlock. We need a global mutex to prevent two + * simultaneous inserts (A into B and B into A) from racing and + * constructing a cycle without either insert observing that it is + * going to. + * It is necessary to acquire multiple "ep->mtx"es at once in the + * case when one epoll fd is added to another. In this case, we + * always acquire the locks in the order of nesting (i.e. after + * epoll_ctl(e1, EPOLL_CTL_ADD, e2), e1->mtx will always be acquired + * before e2->mtx). Since we disallow cycles of epoll file + * descriptors, this ensures that the mutexes are well-ordered. In + * order to communicate this nesting to lockdep, when walking a tree + * of epoll file descriptors, we use the current recursion depth as + * the lockdep subkey. + * 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. + */ + +/* Epoll private bits inside the event mask */ +#define EP_PRIVATE_BITS (EPOLLWAKEUP | EPOLLONESHOT | EPOLLET) + +/* Maximum number of nesting allowed inside epoll sets */ +#define EP_MAX_NESTS 4 + +#define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event)) + +#define EP_UNACTIVE_PTR ((void *) -1L) + +#define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry)) + +struct epoll_filefd { + struct file *file; + int fd; +} __packed; + +/* + * Structure used to track possible nested calls, for too deep recursions + * and loop cycles. + */ +struct nested_call_node { + struct list_head llink; + void *cookie; + void *ctx; +}; + +/* + * This structure is used as collector for nested calls, to check for + * maximum recursion dept and loop cycles. + */ +struct nested_calls { + struct list_head tasks_call_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. + * Avoid increasing the size of this struct, there can be many thousands + * of these on a server and we do not want this to take another cache line. + */ +struct epitem { + union { + /* RB tree node links this structure to the eventpoll RB tree */ + struct rb_node rbn; + /* Used to free the struct epitem */ + struct rcu_head rcu; + }; + + /* List header used to link this structure to the eventpoll ready list */ + struct list_head rdllink; + + /* + * 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; + + /* wakeup_source used when EPOLLWAKEUP is set */ + struct wakeup_source __rcu *ws; + + /* 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 represents the main data structure for the eventpoll + * interface. + */ +struct eventpoll { + /* Protect the access to this structure */ + 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 transferring ready events to userspace w/out + * holding ->lock. + */ + struct epitem *ovflist; + + /* wakeup_source used when ep_scan_ready_list is running */ + struct wakeup_source *ws; + + /* The user that created the eventpoll descriptor */ + struct user_struct *user; + + struct file *file; + + /* used to optimize loop detection check */ + int visited; + struct list_head visited_list_link; +}; + +/* 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" */ + struct epitem *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; +}; + +/* 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/ + */ +/* Maximum number of epoll watched descriptors, per user */ +static long max_user_watches __read_mostly; + +/* + * This mutex is used to serialize ep_free() and eventpoll_release_file(). + */ +static DEFINE_MUTEX(epmutex); + +/* Used to check for epoll file descriptor inclusion loops */ +static struct nested_calls poll_loop_ncalls; + +/* 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; + +/* Slab cache used to allocate "struct eppoll_entry" */ +static struct kmem_cache *pwq_cache __read_mostly; + +/* Visited nodes during ep_loop_check(), so we can unset them when we finish */ +static LIST_HEAD(visited_list); + +/* + * List of files with newly added links, where we may need to limit the number + * of emanating paths. Protected by the epmutex. + */ +static LIST_HEAD(tfile_check_list); + +#ifdef CONFIG_SYSCTL + +#include <linux/sysctl.h> + +static long zero; +static long long_max = LONG_MAX; + +struct ctl_table epoll_table[] = { + { + .procname = "max_user_watches", + .data = &max_user_watches, + .maxlen = sizeof(max_user_watches), + .mode = 0644, + .proc_handler = proc_doulongvec_minmax, + .extra1 = &zero, + .extra2 = &long_max, + }, + { } +}; +#endif /* CONFIG_SYSCTL */ + +static const struct file_operations eventpoll_fops; + +static inline int is_file_epoll(struct file *f) +{ + return f->f_op == &eventpoll_fops; +} + +/* 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); +} + +static inline struct eppoll_entry *ep_pwq_from_wait(wait_queue_t *p) +{ + return container_of(p, struct eppoll_entry, wait); +} + +/* 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_nested_calls_init(struct nested_calls *ncalls) +{ + INIT_LIST_HEAD(&ncalls->tasks_call_list); + spin_lock_init(&ncalls->lock); +} + +/** + * ep_events_available - Checks if ready events might be available. + * + * @ep: Pointer to the eventpoll context. + * + * Returns: Returns a value different than zero if ready events are available, + * or zero otherwise. + */ +static inline int ep_events_available(struct eventpoll *ep) +{ + return !list_empty(&ep->rdllist) || ep->ovflist != EP_UNACTIVE_PTR; +} + +/** + * 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. + * @ctx: This instance context. + * + * Returns: Returns the code returned by the @nproc callback, or -1 if + * the maximum recursion limit has been exceeded. + */ +static int ep_call_nested(struct nested_calls *ncalls, int max_nests, + int (*nproc)(void *, void *, int), void *priv, + void *cookie, void *ctx) +{ + int error, call_nests = 0; + unsigned long flags; + struct list_head *lsthead = &ncalls->tasks_call_list; + struct nested_call_node *tncur; + struct nested_call_node tnode; + + spin_lock_irqsave(&ncalls->lock, flags); + + /* + * 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->ctx == ctx && + (tncur->cookie == cookie || ++call_nests > max_nests)) { + /* + * Ops ... loop detected or maximum nest level reached. + * We abort this wake by breaking the cycle itself. + */ + error = -1; + goto out_unlock; + } + } + + /* Add the current task and cookie to the list */ + tnode.ctx = ctx; + tnode.cookie = cookie; + list_add(&tnode.llink, lsthead); + + spin_unlock_irqrestore(&ncalls->lock, flags); + + /* Call the nested function */ + error = (*nproc)(priv, cookie, call_nests); + + /* Remove the current task from the list */ + spin_lock_irqsave(&ncalls->lock, flags); + list_del(&tnode.llink); +out_unlock: + spin_unlock_irqrestore(&ncalls->lock, flags); + + return error; +} + +/* + * As described in commit 0ccf831cb lockdep: annotate epoll + * the use of wait queues used by epoll is done in a very controlled + * manner. Wake ups can nest inside each other, but are never done + * with the same locking. For example: + * + * dfd = socket(...); + * efd1 = epoll_create(); + * efd2 = epoll_create(); + * epoll_ctl(efd1, EPOLL_CTL_ADD, dfd, ...); + * epoll_ctl(efd2, EPOLL_CTL_ADD, efd1, ...); + * + * When a packet arrives to the device underneath "dfd", the net code will + * issue a wake_up() on its poll wake list. Epoll (efd1) has installed a + * callback wakeup entry on that queue, and the wake_up() performed by the + * "dfd" net code will end up in ep_poll_callback(). At this point epoll + * (efd1) notices that it may have some event ready, so it needs to wake up + * the waiters on its poll wait list (efd2). So it calls ep_poll_safewake() + * that ends up in another wake_up(), after having checked about the + * recursion constraints. That are, no more than EP_MAX_POLLWAKE_NESTS, to + * avoid stack blasting. + * + * When CONFIG_DEBUG_LOCK_ALLOC is enabled, make sure lockdep can handle + * this special case of epoll. + */ +#ifdef CONFIG_DEBUG_LOCK_ALLOC +static inline void ep_wake_up_nested(wait_queue_head_t *wqueue, + unsigned long events, int subclass) +{ + unsigned long flags; + + spin_lock_irqsave_nested(&wqueue->lock, flags, subclass); + wake_up_locked_poll(wqueue, events); + spin_unlock_irqrestore(&wqueue->lock, flags); +} +#else +static inline void ep_wake_up_nested(wait_queue_head_t *wqueue, + unsigned long events, int subclass) +{ + wake_up_poll(wqueue, events); +} +#endif + +static int ep_poll_wakeup_proc(void *priv, void *cookie, int call_nests) +{ + ep_wake_up_nested((wait_queue_head_t *) cookie, POLLIN, + 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) +{ + int this_cpu = get_cpu_light(); + + ep_call_nested(&poll_safewake_ncalls, EP_MAX_NESTS, + ep_poll_wakeup_proc, NULL, wq, (void *) (long) this_cpu); + + put_cpu_light(); +} + +static void ep_remove_wait_queue(struct eppoll_entry *pwq) +{ + wait_queue_head_t *whead; + + rcu_read_lock(); + /* If it is cleared by POLLFREE, it should be rcu-safe */ + whead = rcu_dereference(pwq->whead); + if (whead) + remove_wait_queue(whead, &pwq->wait); + rcu_read_unlock(); +} + +/* + * This function unregisters poll callbacks from the associated file + * descriptor. Must be called with "mtx" held (or "epmutex" if called from + * ep_free). + */ +static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi) +{ + struct list_head *lsthead = &epi->pwqlist; + struct eppoll_entry *pwq; + + while (!list_empty(lsthead)) { + pwq = list_first_entry(lsthead, struct eppoll_entry, llink); + + list_del(&pwq->llink); + ep_remove_wait_queue(pwq); + kmem_cache_free(pwq_cache, pwq); + } +} + +/* call only when ep->mtx is held */ +static inline struct wakeup_source *ep_wakeup_source(struct epitem *epi) +{ + return rcu_dereference_check(epi->ws, lockdep_is_held(&epi->ep->mtx)); +} + +/* call only when ep->mtx is held */ +static inline void ep_pm_stay_awake(struct epitem *epi) +{ + struct wakeup_source *ws = ep_wakeup_source(epi); + + if (ws) + __pm_stay_awake(ws); +} + +static inline bool ep_has_wakeup_source(struct epitem *epi) +{ + return rcu_access_pointer(epi->ws) ? true : false; +} + +/* call when ep->mtx cannot be held (ep_poll_callback) */ +static inline void ep_pm_stay_awake_rcu(struct epitem *epi) +{ + struct wakeup_source *ws; + + rcu_read_lock(); + ws = rcu_dereference(epi->ws); + if (ws) + __pm_stay_awake(ws); + rcu_read_unlock(); +} + +/** + * 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. + * @depth: The current depth of recursive f_op->poll calls. + * @ep_locked: caller already holds ep->mtx + * + * Returns: The same integer error code returned by the @sproc callback. + */ +static int ep_scan_ready_list(struct eventpoll *ep, + int (*sproc)(struct eventpoll *, + struct list_head *, void *), + void *priv, int depth, bool ep_locked) +{ + int error, pwake = 0; + unsigned long flags; + struct epitem *epi, *nepi; + LIST_HEAD(txlist); + + /* + * We need to lock this because we could be hit by + * eventpoll_release_file() and epoll_ctl(). + */ + + if (!ep_locked) + mutex_lock_nested(&ep->mtx, depth); + + /* + * 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_init(&ep->rdllist, &txlist); + 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); + ep_pm_stay_awake(epi); + } + } + /* + * 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); + __pm_relax(ep->ws); + + 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); + + if (!ep_locked) + mutex_unlock(&ep->mtx); + + /* We have to call this outside the lock */ + if (pwake) + ep_poll_safewake(&ep->poll_wait); + + return error; +} + +static void epi_rcu_free(struct rcu_head *head) +{ + struct epitem *epi = container_of(head, struct epitem, rcu); + kmem_cache_free(epi_cache, epi); +} + +/* + * Removes a "struct epitem" from the eventpoll RB tree and deallocates + * all the associated resources. Must be called with "mtx" held. + */ +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_lock); + list_del_rcu(&epi->fllink); + spin_unlock(&file->f_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); + + wakeup_source_unregister(ep_wakeup_source(epi)); + /* + * At this point it is safe to free the eventpoll item. Use the union + * field epi->rcu, since we are trying to minimize the size of + * 'struct epitem'. The 'rbn' field is no longer in use. Protected by + * ep->mtx. The rcu read side, reverse_path_check_proc(), does not make + * use of the rbn field. + */ + call_rcu(&epi->rcu, epi_rcu_free); + + atomic_long_dec(&ep->user->epoll_watches); + + 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(&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 sufficient 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); + cond_resched(); + } + + /* + * 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". + * We do not need to lock ep->mtx, either, we only do it to prevent + * a lockdep warning. + */ + mutex_lock(&ep->mtx); + while ((rbp = rb_first(&ep->rbr)) != NULL) { + epi = rb_entry(rbp, struct epitem, rbn); + ep_remove(ep, epi); + cond_resched(); + } + mutex_unlock(&ep->mtx); + + mutex_unlock(&epmutex); + mutex_destroy(&ep->mtx); + free_uid(ep->user); + wakeup_source_unregister(ep->ws); + kfree(ep); +} + +static int ep_eventpoll_release(struct inode *inode, struct file *file) +{ + struct eventpoll *ep = file->private_data; + + if (ep) + ep_free(ep); + + return 0; +} + +static inline unsigned int ep_item_poll(struct epitem *epi, poll_table *pt) +{ + pt->_key = epi->event.events; + + return epi->ffd.file->f_op->poll(epi->ffd.file, pt) & epi->event.events; +} + +static int ep_read_events_proc(struct eventpoll *ep, struct list_head *head, + void *priv) +{ + struct epitem *epi, *tmp; + poll_table pt; + + init_poll_funcptr(&pt, NULL); + + list_for_each_entry_safe(epi, tmp, head, rdllink) { + if (ep_item_poll(epi, &pt)) + 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. + */ + __pm_relax(ep_wakeup_source(epi)); + list_del_init(&epi->rdllink); + } + } + + return 0; +} + +static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead, + poll_table *pt); + +struct readyevents_arg { + struct eventpoll *ep; + bool locked; +}; + +static int ep_poll_readyevents_proc(void *priv, void *cookie, int call_nests) +{ + struct readyevents_arg *arg = priv; + + return ep_scan_ready_list(arg->ep, ep_read_events_proc, NULL, + call_nests + 1, arg->locked); +} + +static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait) +{ + int pollflags; + struct eventpoll *ep = file->private_data; + struct readyevents_arg arg; + + /* + * During ep_insert() we already hold the ep->mtx for the tfile. + * Prevent re-aquisition. + */ + arg.locked = wait && (wait->_qproc == ep_ptable_queue_proc); + arg.ep = ep; + + /* Insert inside our poll wait queue */ + poll_wait(file, &ep->poll_wait, wait); + + /* + * 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, &arg, ep, current); + + return pollflags != -1 ? pollflags : 0; +} + +#ifdef CONFIG_PROC_FS +static void ep_show_fdinfo(struct seq_file *m, struct file *f) +{ + struct eventpoll *ep = f->private_data; + struct rb_node *rbp; + + mutex_lock(&ep->mtx); + for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) { + struct epitem *epi = rb_entry(rbp, struct epitem, rbn); + + seq_printf(m, "tfd: %8d events: %8x data: %16llx\n", + epi->ffd.fd, epi->event.events, + (long long)epi->event.data); + if (seq_has_overflowed(m)) + break; + } + mutex_unlock(&ep->mtx); +} +#endif + +/* File callbacks that implement the eventpoll file behaviour */ +static const struct file_operations eventpoll_fops = { +#ifdef CONFIG_PROC_FS + .show_fdinfo = ep_show_fdinfo, +#endif + .release = ep_eventpoll_release, + .poll = ep_eventpoll_poll, + .llseek = noop_llseek, +}; + +/* + * 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 eventpoll *ep; + struct epitem *epi, *next; + + /* + * 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 no one is using this file anymore. + * 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 + * "ep->mtx" after "epmutex" because ep_remove() requires it when called + * from anywhere but ep_free(). + * + * Besides, ep_remove() acquires the lock, so we can't hold it here. + */ + mutex_lock(&epmutex); + list_for_each_entry_safe(epi, next, &file->f_ep_links, fllink) { + ep = epi->ep; + mutex_lock_nested(&ep->mtx, 0); + ep_remove(ep, epi); + mutex_unlock(&ep->mtx); + } + mutex_unlock(&epmutex); +} + +static int ep_alloc(struct eventpoll **pep) +{ + int error; + struct user_struct *user; + struct eventpoll *ep; + + user = get_current_user(); + error = -ENOMEM; + ep = kzalloc(sizeof(*ep), GFP_KERNEL); + if (unlikely(!ep)) + goto free_uid; + + 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; + ep->user = user; + + *pep = ep; + + return 0; + +free_uid: + free_uid(user); + return error; +} + +/* + * 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; + } + } + + return epir; +} + +/* + * This is the callback that is passed to the wait queue wakeup + * mechanism. 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; + + if ((unsigned long)key & POLLFREE) { + ep_pwq_from_wait(wait)->whead = NULL; + /* + * whead = NULL above can race with ep_remove_wait_queue() + * which can do another remove_wait_queue() after us, so we + * can't use __remove_wait_queue(). whead->lock is held by + * the caller. + */ + list_del_init(&wait->task_list); + } + + 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; + + /* + * Check the events coming with the callback. At this stage, not + * every device reports the events in the "key" parameter of the + * callback. We need to be able to handle both cases here, hence the + * test for "key" != NULL before the event match test. + */ + if (key && !((unsigned long) key & epi->event.events)) + goto out_unlock; + + /* + * If we are transferring 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 happen 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; + if (epi->ws) { + /* + * Activate ep->ws since epi->ws may get + * deactivated at any time. + */ + __pm_stay_awake(ep->ws); + } + + } + goto out_unlock; + } + + /* If this file is already in the ready list we exit soon */ + if (!ep_is_linked(&epi->rdllink)) { + list_add_tail(&epi->rdllink, &ep->rdllist); + ep_pm_stay_awake_rcu(epi); + } + + /* + * 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(&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); +} + + + +#define PATH_ARR_SIZE 5 +/* + * These are the number paths of length 1 to 5, that we are allowing to emanate + * from a single file of interest. For example, we allow 1000 paths of length + * 1, to emanate from each file of interest. This essentially represents the + * potential wakeup paths, which need to be limited in order to avoid massive + * uncontrolled wakeup storms. The common use case should be a single ep which + * is connected to n file sources. In this case each file source has 1 path + * of length 1. Thus, the numbers below should be more than sufficient. These + * path limits are enforced during an EPOLL_CTL_ADD operation, since a modify + * and delete can't add additional paths. Protected by the epmutex. + */ +static const int path_limits[PATH_ARR_SIZE] = { 1000, 500, 100, 50, 10 }; +static int path_count[PATH_ARR_SIZE]; + +static int path_count_inc(int nests) +{ + /* Allow an arbitrary number of depth 1 paths */ + if (nests == 0) + return 0; + + if (++path_count[nests] > path_limits[nests]) + return -1; + return 0; +} + +static void path_count_init(void) +{ + int i; + + for (i = 0; i < PATH_ARR_SIZE; i++) + path_count[i] = 0; +} + +static int reverse_path_check_proc(void *priv, void *cookie, int call_nests) +{ + int error = 0; + struct file *file = priv; + struct file *child_file; + struct epitem *epi; + + /* CTL_DEL can remove links here, but that can't increase our count */ + rcu_read_lock(); + list_for_each_entry_rcu(epi, &file->f_ep_links, fllink) { + child_file = epi->ep->file; + if (is_file_epoll(child_file)) { + if (list_empty(&child_file->f_ep_links)) { + if (path_count_inc(call_nests)) { + error = -1; + break; + } + } else { + error = ep_call_nested(&poll_loop_ncalls, + EP_MAX_NESTS, + reverse_path_check_proc, + child_file, child_file, + current); + } + if (error != 0) + break; + } else { + printk(KERN_ERR "reverse_path_check_proc: " + "file is not an ep!\n"); + } + } + rcu_read_unlock(); + return error; +} + +/** + * reverse_path_check - The tfile_check_list is list of file *, which have + * links that are proposed to be newly added. We need to + * make sure that those added links don't add too many + * paths such that we will spend all our time waking up + * eventpoll objects. + * + * Returns: Returns zero if the proposed links don't create too many paths, + * -1 otherwise. + */ +static int reverse_path_check(void) +{ + int error = 0; + struct file *current_file; + + /* let's call this for all tfiles */ + list_for_each_entry(current_file, &tfile_check_list, f_tfile_llink) { + path_count_init(); + error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS, + reverse_path_check_proc, current_file, + current_file, current); + if (error) + break; + } + return error; +} + +static int ep_create_wakeup_source(struct epitem *epi) +{ + const char *name; + struct wakeup_source *ws; + + if (!epi->ep->ws) { + epi->ep->ws = wakeup_source_register("eventpoll"); + if (!epi->ep->ws) + return -ENOMEM; + } + + name = epi->ffd.file->f_path.dentry->d_name.name; + ws = wakeup_source_register(name); + + if (!ws) + return -ENOMEM; + rcu_assign_pointer(epi->ws, ws); + + return 0; +} + +/* rare code path, only used when EPOLL_CTL_MOD removes a wakeup source */ +static noinline void ep_destroy_wakeup_source(struct epitem *epi) +{ + struct wakeup_source *ws = ep_wakeup_source(epi); + + RCU_INIT_POINTER(epi->ws, NULL); + + /* + * wait for ep_pm_stay_awake_rcu to finish, synchronize_rcu is + * used internally by wakeup_source_remove, too (called by + * wakeup_source_unregister), so we cannot use call_rcu + */ + synchronize_rcu(); + wakeup_source_unregister(ws); +} + +/* + * Must be called with "mtx" held. + */ +static int ep_insert(struct eventpoll *ep, struct epoll_event *event, + struct file *tfile, int fd, int full_check) +{ + int error, revents, pwake = 0; + unsigned long flags; + long user_watches; + struct epitem *epi; + struct ep_pqueue epq; + + user_watches = atomic_long_read(&ep->user->epoll_watches); + if (unlikely(user_watches >= max_user_watches)) + return -ENOSPC; + if (!(epi = kmem_cache_alloc(epi_cache, GFP_KERNEL))) + return -ENOMEM; + + /* 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; + if (epi->event.events & EPOLLWAKEUP) { + error = ep_create_wakeup_source(epi); + if (error) + goto error_create_wakeup_source; + } else { + RCU_INIT_POINTER(epi->ws, NULL); + } + + /* 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 = ep_item_poll(epi, &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. + */ + error = -ENOMEM; + 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_lock); + list_add_tail_rcu(&epi->fllink, &tfile->f_ep_links); + spin_unlock(&tfile->f_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); + + /* now check if we've created too many backpaths */ + error = -EINVAL; + if (full_check && reverse_path_check()) + goto error_remove_epi; + + /* We have to drop the new item inside our item list to keep track of it */ + 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); + ep_pm_stay_awake(epi); + + /* 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); + + atomic_long_inc(&ep->user->epoll_watches); + + /* We have to call this outside the lock */ + if (pwake) + ep_poll_safewake(&ep->poll_wait); + + return 0; + +error_remove_epi: + spin_lock(&tfile->f_lock); + list_del_rcu(&epi->fllink); + spin_unlock(&tfile->f_lock); + + rb_erase(&epi->rbn, &ep->rbr); + +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); + + wakeup_source_unregister(ep_wakeup_source(epi)); + +error_create_wakeup_source: + kmem_cache_free(epi_cache, epi); + + 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; + poll_table pt; + + init_poll_funcptr(&pt, NULL); + + /* + * Set the new event interest mask before calling f_op->poll(); + * otherwise we might miss an event that happens between the + * f_op->poll() call and the new event set registering. + */ + epi->event.events = event->events; /* need barrier below */ + epi->event.data = event->data; /* protected by mtx */ + if (epi->event.events & EPOLLWAKEUP) { + if (!ep_has_wakeup_source(epi)) + ep_create_wakeup_source(epi); + } else if (ep_has_wakeup_source(epi)) { + ep_destroy_wakeup_source(epi); + } + + /* + * The following barrier has two effects: + * + * 1) Flush epi changes above to other CPUs. This ensures + * we do not miss events from ep_poll_callback if an + * event occurs immediately after we call f_op->poll(). + * We need this because we did not take ep->lock while + * changing epi above (but ep_poll_callback does take + * ep->lock). + * + * 2) We also need to ensure we do not miss _past_ events + * when calling f_op->poll(). This barrier also + * pairs with the barrier in wq_has_sleeper (see + * comments for wq_has_sleeper). + * + * This barrier will now guarantee ep_poll_callback or f_op->poll + * (or both) will notice the readiness of an item. + */ + smp_mb(); + + /* + * 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 = ep_item_poll(epi, &pt); + + /* + * If the item is "hot" and it is not registered inside the ready + * list, push it inside. + */ + if (revents & event->events) { + spin_lock_irq(&ep->lock); + if (!ep_is_linked(&epi->rdllink)) { + list_add_tail(&epi->rdllink, &ep->rdllist); + ep_pm_stay_awake(epi); + + /* 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_irq(&ep->lock); + } + + /* We have to call this outside the lock */ + if (pwake) + ep_poll_safewake(&ep->poll_wait); + + return 0; +} + +static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head, + void *priv) +{ + struct ep_send_events_data *esed = priv; + int eventcnt; + unsigned int revents; + struct epitem *epi; + struct epoll_event __user *uevent; + struct wakeup_source *ws; + poll_table pt; + + init_poll_funcptr(&pt, NULL); + + /* + * 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); + + /* + * Activate ep->ws before deactivating epi->ws to prevent + * triggering auto-suspend here (in case we reactive epi->ws + * below). + * + * This could be rearranged to delay the deactivation of epi->ws + * instead, but then epi->ws would temporarily be out of sync + * with ep_is_linked(). + */ + ws = ep_wakeup_source(epi); + if (ws) { + if (ws->active) + __pm_stay_awake(ep->ws); + __pm_relax(ws); + } + + list_del_init(&epi->rdllink); + + revents = ep_item_poll(epi, &pt); + + /* + * 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)) { + list_add(&epi->rdllink, head); + ep_pm_stay_awake(epi); + 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, no one 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); + ep_pm_stay_awake(epi); + } + } + } + + return eventcnt; +} + +static int ep_send_events(struct eventpoll *ep, + struct epoll_event __user *events, int maxevents) +{ + struct ep_send_events_data esed; + + esed.maxevents = maxevents; + esed.events = events; + + return ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0, false); +} + +static inline struct timespec ep_set_mstimeout(long ms) +{ + struct timespec now, ts = { + .tv_sec = ms / MSEC_PER_SEC, + .tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC), + }; + + ktime_get_ts(&now); + return timespec_add_safe(now, ts); +} + +/** + * ep_poll - Retrieves ready events, and delivers them to the caller supplied + * event buffer. + * + * @ep: Pointer to the eventpoll context. + * @events: Pointer to the userspace buffer where the ready events should be + * stored. + * @maxevents: Size (in terms of number of events) of the caller event buffer. + * @timeout: Maximum timeout for the ready events fetch operation, in + * milliseconds. If the @timeout is zero, the function will not block, + * while if the @timeout is less than zero, the function will block + * until at least one event has been retrieved (or an error + * occurred). + * + * Returns: Returns the number of ready events which have been fetched, or an + * error code, in case of error. + */ +static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, + int maxevents, long timeout) +{ + int res = 0, eavail, timed_out = 0; + unsigned long flags; + long slack = 0; + wait_queue_t wait; + ktime_t expires, *to = NULL; + + if (timeout > 0) { + struct timespec end_time = ep_set_mstimeout(timeout); + + slack = select_estimate_accuracy(&end_time); + to = &expires; + *to = timespec_to_ktime(end_time); + } else if (timeout == 0) { + /* + * Avoid the unnecessary trip to the wait queue loop, if the + * caller specified a non blocking operation. + */ + timed_out = 1; + spin_lock_irqsave(&ep->lock, flags); + goto check_events; + } + +fetch_events: + spin_lock_irqsave(&ep->lock, flags); + + if (!ep_events_available(ep)) { + /* + * 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); + __add_wait_queue_exclusive(&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 (ep_events_available(ep) || timed_out) + break; + if (signal_pending(current)) { + res = -EINTR; + break; + } + + spin_unlock_irqrestore(&ep->lock, flags); + if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS)) + timed_out = 1; + + spin_lock_irqsave(&ep->lock, flags); + } + + __remove_wait_queue(&ep->wq, &wait); + __set_current_state(TASK_RUNNING); + } +check_events: + /* Is it worth to try to dig for events ? */ + eavail = ep_events_available(ep); + + 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)) && !timed_out) + goto fetch_events; + + return res; +} + +/** + * ep_loop_check_proc - Callback function to be passed to the @ep_call_nested() + * API, to verify that adding an epoll file inside another + * epoll structure, does not violate the constraints, in + * terms of closed loops, or too deep chains (which can + * result in excessive stack usage). + * + * @priv: Pointer to the epoll file to be currently checked. + * @cookie: Original cookie for this call. This is the top-of-the-chain epoll + * data structure pointer. + * @call_nests: Current dept of the @ep_call_nested() call stack. + * + * Returns: Returns zero if adding the epoll @file inside current epoll + * structure @ep does not violate the constraints, or -1 otherwise. + */ +static int ep_loop_check_proc(void *priv, void *cookie, int call_nests) +{ + int error = 0; + struct file *file = priv; + struct eventpoll *ep = file->private_data; + struct eventpoll *ep_tovisit; + struct rb_node *rbp; + struct epitem *epi; + + mutex_lock_nested(&ep->mtx, call_nests + 1); + ep->visited = 1; + list_add(&ep->visited_list_link, &visited_list); + for (rbp = rb_first(&ep->rbr); rbp; rbp = rb_next(rbp)) { + epi = rb_entry(rbp, struct epitem, rbn); + if (unlikely(is_file_epoll(epi->ffd.file))) { + ep_tovisit = epi->ffd.file->private_data; + if (ep_tovisit->visited) + continue; + error = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS, + ep_loop_check_proc, epi->ffd.file, + ep_tovisit, current); + if (error != 0) + break; + } else { + /* + * If we've reached a file that is not associated with + * an ep, then we need to check if the newly added + * links are going to add too many wakeup paths. We do + * this by adding it to the tfile_check_list, if it's + * not already there, and calling reverse_path_check() + * during ep_insert(). + */ + if (list_empty(&epi->ffd.file->f_tfile_llink)) + list_add(&epi->ffd.file->f_tfile_llink, + &tfile_check_list); + } + } + mutex_unlock(&ep->mtx); + + return error; +} + +/** + * ep_loop_check - Performs a check to verify that adding an epoll file (@file) + * another epoll file (represented by @ep) does not create + * closed loops or too deep chains. + * + * @ep: Pointer to the epoll private data structure. + * @file: Pointer to the epoll file to be checked. + * + * Returns: Returns zero if adding the epoll @file inside current epoll + * structure @ep does not violate the constraints, or -1 otherwise. + */ +static int ep_loop_check(struct eventpoll *ep, struct file *file) +{ + int ret; + struct eventpoll *ep_cur, *ep_next; + + ret = ep_call_nested(&poll_loop_ncalls, EP_MAX_NESTS, + ep_loop_check_proc, file, ep, current); + /* clear visited list */ + list_for_each_entry_safe(ep_cur, ep_next, &visited_list, + visited_list_link) { + ep_cur->visited = 0; + list_del(&ep_cur->visited_list_link); + } + return ret; +} + +static void clear_tfile_check_list(void) +{ + struct file *file; + + /* first clear the tfile_check_list */ + while (!list_empty(&tfile_check_list)) { + file = list_first_entry(&tfile_check_list, struct file, + f_tfile_llink); + list_del_init(&file->f_tfile_llink); + } + INIT_LIST_HEAD(&tfile_check_list); +} + +/* + * Open an eventpoll file descriptor. + */ +SYSCALL_DEFINE1(epoll_create1, int, flags) +{ + int error, fd; + struct eventpoll *ep = NULL; + struct file *file; + + /* Check the EPOLL_* constant for consistency. */ + BUILD_BUG_ON(EPOLL_CLOEXEC != O_CLOEXEC); + + if (flags & ~EPOLL_CLOEXEC) + return -EINVAL; + /* + * Create the internal data structure ("struct eventpoll"). + */ + error = ep_alloc(&ep); + if (error < 0) + return error; + /* + * Creates all the items needed to setup an eventpoll file. That is, + * a file structure and a free file descriptor. + */ + fd = get_unused_fd_flags(O_RDWR | (flags & O_CLOEXEC)); + if (fd < 0) { + error = fd; + goto out_free_ep; + } + file = anon_inode_getfile("[eventpoll]", &eventpoll_fops, ep, + O_RDWR | (flags & O_CLOEXEC)); + if (IS_ERR(file)) { + error = PTR_ERR(file); + goto out_free_fd; + } + ep->file = file; + fd_install(fd, file); + return fd; + +out_free_fd: + put_unused_fd(fd); +out_free_ep: + ep_free(ep); + return error; +} + +SYSCALL_DEFINE1(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. + */ +SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd, + struct epoll_event __user *, event) +{ + int error; + int full_check = 0; + struct fd f, tf; + struct eventpoll *ep; + struct epitem *epi; + struct epoll_event epds; + struct eventpoll *tep = NULL; + + error = -EFAULT; + if (ep_op_has_event(op) && + copy_from_user(&epds, event, sizeof(struct epoll_event))) + goto error_return; + + error = -EBADF; + f = fdget(epfd); + if (!f.file) + goto error_return; + + /* Get the "struct file *" for the target file */ + tf = fdget(fd); + if (!tf.file) + goto error_fput; + + /* The target file descriptor must support poll */ + error = -EPERM; + if (!tf.file->f_op->poll) + goto error_tgt_fput; + + /* Check if EPOLLWAKEUP is allowed */ + if (ep_op_has_event(op)) + ep_take_care_of_epollwakeup(&epds); + + /* + * 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 (f.file == tf.file || !is_file_epoll(f.file)) + goto error_tgt_fput; + + /* + * At this point it is safe to assume that the "private_data" contains + * our own data structure. + */ + ep = f.file->private_data; + + /* + * When we insert an epoll file descriptor, inside another epoll file + * descriptor, there is the change of creating closed loops, which are + * better be handled here, than in more critical paths. While we are + * checking for loops we also determine the list of files reachable + * and hang them on the tfile_check_list, so we can check that we + * haven't created too many possible wakeup paths. + * + * We do not need to take the global 'epumutex' on EPOLL_CTL_ADD when + * the epoll file descriptor is attaching directly to a wakeup source, + * unless the epoll file descriptor is nested. The purpose of taking the + * 'epmutex' on add is to prevent complex toplogies such as loops and + * deep wakeup paths from forming in parallel through multiple + * EPOLL_CTL_ADD operations. + */ + mutex_lock_nested(&ep->mtx, 0); + if (op == EPOLL_CTL_ADD) { + if (!list_empty(&f.file->f_ep_links) || + is_file_epoll(tf.file)) { + full_check = 1; + mutex_unlock(&ep->mtx); + mutex_lock(&epmutex); + if (is_file_epoll(tf.file)) { + error = -ELOOP; + if (ep_loop_check(ep, tf.file) != 0) { + clear_tfile_check_list(); + goto error_tgt_fput; + } + } else + list_add(&tf.file->f_tfile_llink, + &tfile_check_list); + mutex_lock_nested(&ep->mtx, 0); + if (is_file_epoll(tf.file)) { + tep = tf.file->private_data; + mutex_lock_nested(&tep->mtx, 1); + } + } + } + + /* + * 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, tf.file, fd); + + error = -EINVAL; + switch (op) { + case EPOLL_CTL_ADD: + if (!epi) { + epds.events |= POLLERR | POLLHUP; + error = ep_insert(ep, &epds, tf.file, fd, full_check); + } else + error = -EEXIST; + if (full_check) + clear_tfile_check_list(); + 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; + } + if (tep != NULL) + mutex_unlock(&tep->mtx); + mutex_unlock(&ep->mtx); + +error_tgt_fput: + if (full_check) + mutex_unlock(&epmutex); + + fdput(tf); +error_fput: + fdput(f); +error_return: + + return error; +} + +/* + * Implement the event wait interface for the eventpoll file. It is the kernel + * part of the user space epoll_wait(2). + */ +SYSCALL_DEFINE4(epoll_wait, int, epfd, struct epoll_event __user *, events, + int, maxevents, int, timeout) +{ + int error; + struct fd f; + struct eventpoll *ep; + + /* 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))) + return -EFAULT; + + /* Get the "struct file *" for the eventpoll file */ + f = fdget(epfd); + if (!f.file) + return -EBADF; + + /* + * 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(f.file)) + goto error_fput; + + /* + * At this point it is safe to assume that the "private_data" contains + * our own data structure. + */ + ep = f.file->private_data; + + /* Time to fish for events ... */ + error = ep_poll(ep, events, maxevents, timeout); + +error_fput: + fdput(f); + return error; +} + +/* + * Implement the event wait interface for the eventpoll file. It is the kernel + * part of the user space epoll_pwait(2). + */ +SYSCALL_DEFINE6(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; + sigsaved = current->blocked; + set_current_blocked(&ksigmask); + } + + 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 + set_current_blocked(&sigsaved); + } + + return error; +} + +#ifdef CONFIG_COMPAT +COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd, + struct epoll_event __user *, events, + int, maxevents, int, timeout, + const compat_sigset_t __user *, sigmask, + compat_size_t, sigsetsize) +{ + long err; + compat_sigset_t csigmask; + 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(compat_sigset_t)) + return -EINVAL; + if (copy_from_user(&csigmask, sigmask, sizeof(csigmask))) + return -EFAULT; + sigset_from_compat(&ksigmask, &csigmask); + sigsaved = current->blocked; + set_current_blocked(&ksigmask); + } + + err = 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 (err == -EINTR) { + memcpy(¤t->saved_sigmask, &sigsaved, + sizeof(sigsaved)); + set_restore_sigmask(); + } else + set_current_blocked(&sigsaved); + } + + return err; +} +#endif + +static int __init eventpoll_init(void) +{ + struct sysinfo si; + + si_meminfo(&si); + /* + * Allows top 4% of lomem to be allocated for epoll watches (per user). + */ + max_user_watches = (((si.totalram - si.totalhigh) / 25) << PAGE_SHIFT) / + EP_ITEM_COST; + BUG_ON(max_user_watches < 0); + + /* + * Initialize the structure used to perform epoll file descriptor + * inclusion loops checks. + */ + ep_nested_calls_init(&poll_loop_ncalls); + + /* Initialize the structure used to perform safe poll wait head wake ups */ + 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); + + /* + * We can have many thousands of epitems, so prevent this from + * using an extra cache line on 64-bit (and smaller) CPUs + */ + BUILD_BUG_ON(sizeof(void *) <= 8 && sizeof(struct epitem) > 128); + + /* Allocates slab cache used to allocate "struct epitem" items */ + epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem), + 0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL); + + /* Allocates slab cache used to allocate "struct eppoll_entry" */ + pwq_cache = kmem_cache_create("eventpoll_pwq", + sizeof(struct eppoll_entry), 0, SLAB_PANIC, NULL); + + return 0; +} +fs_initcall(eventpoll_init); |