diff options
| -rw-r--r-- | fs/eventpoll.c | 322 |
1 files changed, 166 insertions, 156 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 1aad34e..1dbedc7 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -26,7 +26,6 @@ #include <linux/hash.h> #include <linux/spinlock.h> #include <linux/syscalls.h> -#include <linux/rwsem.h> #include <linux/rbtree.h> #include <linux/wait.h> #include <linux/eventpoll.h> @@ -39,14 +38,13 @@ #include <asm/io.h> #include <asm/mman.h> #include <asm/atomic.h> -#include <asm/semaphore.h> /* * LOCKING: * There are three level of locking required by epoll : * * 1) epmutex (mutex) - * 2) ep->sem (rw_semaphore) + * 2) ep->mtx (mutes) * 3) ep->lock (rw_lock) * * The acquire order is the one listed above, from 1 to 3. @@ -57,20 +55,20 @@ * 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 - * read-write semaphore (ep->sem). It is acquired on read during - * the event transfer loop and in write during epoll_ctl(EPOLL_CTL_DEL) - * and during eventpoll_release_file(). Then we also need a global - * semaphore to serialize eventpoll_release_file() and ep_free(). - * This semaphore is acquired by ep_free() during the epoll file + * 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->sem" and to use the global - * semaphore "epmutex" (together with "ep->lock") to have it working, - * but having "ep->sem" will make the interface more scalable. + * 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->sem" will guarantee - * a greater scalability. + * normal operations the epoll private "ep->mtx" will guarantee + * a better scalability. */ #define DEBUG_EPOLL 0 @@ -102,6 +100,8 @@ #define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event)) +#define EP_UNACTIVE_PTR ((void *) -1L) + struct epoll_filefd { struct file *file; int fd; @@ -111,7 +111,7 @@ struct epoll_filefd { * Node that is linked into the "wake_task_list" member of the "struct poll_safewake". * It is used to keep track on all tasks that are currently inside the wake_up() code * to 1) short-circuit the one coming from the same task and same wait queue head - * ( loop ) 2) allow a maximum number of epoll descriptors inclusion nesting + * (loop) 2) allow a maximum number of epoll descriptors inclusion nesting * 3) let go the ones coming from other tasks. */ struct wake_task_node { @@ -130,6 +130,48 @@ struct poll_safewake { }; /* + * 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; + + /* 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; + + /* The structure that describe the interested events and the source fd */ + struct epoll_event event; + + /* + * Used to keep track of the usage count of the structure. This avoids + * that the structure will desappear from underneath our processing. + */ + atomic_t usecnt; + + /* List header used to link this item to the "struct file" items list */ + struct list_head fllink; + + /* + * Works together "struct eventpoll"->ovflist in keeping the + * single linked chain of items. + */ + struct epitem *next; +}; + +/* * This structure is stored inside the "private_data" member of the file * structure and rapresent the main data sructure for the eventpoll * interface. @@ -139,12 +181,12 @@ struct eventpoll { rwlock_t lock; /* - * This semaphore is used to ensure that files are not removed - * while epoll is using them. This is read-held during the event - * collection loop and it is write-held during the file cleanup - * path, the epoll file exit code and the ctl operations. + * 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 rw_semaphore sem; + struct mutex mtx; /* Wait queue used by sys_epoll_wait() */ wait_queue_head_t wq; @@ -157,6 +199,13 @@ struct eventpoll { /* 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 */ @@ -177,42 +226,6 @@ struct eppoll_entry { wait_queue_head_t *whead; }; -/* - * 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; - - /* 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; - - /* The structure that describe the interested events and the source fd */ - struct epoll_event event; - - /* - * Used to keep track of the usage count of the structure. This avoids - * that the structure will desappear from underneath our processing. - */ - atomic_t usecnt; - - /* List header used to link this item to the "struct file" items list */ - struct list_head fllink; -}; - /* Wrapper struct used by poll queueing */ struct ep_pqueue { poll_table pt; @@ -220,7 +233,7 @@ struct ep_pqueue { }; /* - * This semaphore is used to serialize ep_free() and eventpoll_release_file(). + * This mutex is used to serialize ep_free() and eventpoll_release_file(). */ static struct mutex epmutex; @@ -506,7 +519,7 @@ static void ep_free(struct eventpoll *ep) /* * 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->sem" here because the epoll file + * 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. @@ -525,7 +538,7 @@ static void ep_free(struct eventpoll *ep) /* * 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 - * write-holding "sem" we can be sure that no file cleanup code will hit + * 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)) != 0) { @@ -534,6 +547,8 @@ static void ep_free(struct eventpoll *ep) } mutex_unlock(&epmutex); + + mutex_destroy(&ep->mtx); } static int ep_eventpoll_release(struct inode *inode, struct file *file) @@ -594,9 +609,9 @@ void eventpoll_release_file(struct file *file) * 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. - * The only hit might come from ep_free() but by holding the semaphore + * The only hit might come from ep_free() but by holding the mutex * will correctly serialize the operation. We do need to acquire - * "ep->sem" after "epmutex" because ep_remove() requires it when called + * "ep->mtx" after "epmutex" because ep_remove() requires it when called * from anywhere but ep_free(). */ mutex_lock(&epmutex); @@ -606,9 +621,9 @@ void eventpoll_release_file(struct file *file) ep = epi->ep; list_del_init(&epi->fllink); - down_write(&ep->sem); + mutex_lock(&ep->mtx); ep_remove(ep, epi); - up_write(&ep->sem); + mutex_unlock(&ep->mtx); } mutex_unlock(&epmutex); @@ -622,11 +637,12 @@ static int ep_alloc(struct eventpoll **pep) return -ENOMEM; rwlock_init(&ep->lock); - init_rwsem(&ep->sem); + 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; @@ -695,7 +711,21 @@ static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *k * until the next EPOLL_CTL_MOD will be issued. */ if (!(epi->event.events & ~EP_PRIVATE_BITS)) - goto is_disabled; + 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)) @@ -714,7 +744,7 @@ is_linked: if (waitqueue_active(&ep->poll_wait)) pwake++; -is_disabled: +out_unlock: write_unlock_irqrestore(&ep->lock, flags); /* We have to call this outside the lock */ @@ -788,6 +818,7 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event, epi->event = *event; atomic_set(&epi->usecnt, 1); epi->nwait = 0; + epi->next = EP_UNACTIVE_PTR; /* Initialize the poll table using the queue callback */ epq.epi = epi; @@ -920,36 +951,50 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even return 0; } -/* - * This function is called without holding the "ep->lock" since the call to - * __copy_to_user() might sleep, and also f_op->poll() might reenable the IRQ - * because of the way poll() is traditionally implemented in Linux. - */ -static int ep_send_events(struct eventpoll *ep, struct list_head *txlist, - struct epoll_event __user *events, int maxevents) +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; - struct list_head injlist; + struct epitem *epi, *nepi; + struct list_head txlist; + + INIT_LIST_HEAD(&txlist); - INIT_LIST_HEAD(&injlist); + /* + * 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. + */ + write_lock_irqsave(&ep->lock, flags); + list_splice(&ep->rdllist, &txlist); + INIT_LIST_HEAD(&ep->rdllist); + ep->ovflist = NULL; + write_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 "sem" in - * read. + * 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); - prefetch(epi->rdllink.next); + 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 "sem" in read and this will - * guarantee that both the file and the item will not vanish. + * 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; @@ -957,8 +1002,8 @@ static int ep_send_events(struct eventpoll *ep, struct list_head *txlist, /* * Is the event mask intersect the caller-requested one, * deliver the event to userspace. Again, we are holding - * "sem" in read, so no operations coming from userspace - * can change the item. + * "mtx", so no operations coming from userspace can change + * the item. */ if (revents) { if (__put_user(revents, @@ -970,49 +1015,47 @@ static int ep_send_events(struct eventpoll *ep, struct list_head *txlist, epi->event.events &= EP_PRIVATE_BITS; eventcnt++; } - /* - * This is tricky. We are holding the "sem" in read, and this - * means that the operations that can change the "linked" status - * of the epoll item (epi->rbn and epi->rdllink), cannot touch - * them. Also, since we are "linked" from a epi->rdllink POV - * (the item is linked to our transmission list we just - * spliced), the ep_poll_callback() cannot touch us either, - * because of the check present in there. Another parallel - * epoll_wait() will not get the same result set, since we - * spliced the ready list before. Note that list_del() still - * shows the item as linked to the test in ep_poll_callback(). + * 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. */ - list_del(&epi->rdllink); if (!(epi->event.events & EPOLLET) && - (revents & epi->event.events)) - list_add_tail(&epi->rdllink, &injlist); - else { - /* - * Be sure the item is totally detached before re-init - * the list_head. After INIT_LIST_HEAD() is committed, - * the ep_poll_callback() can requeue the item again, - * but we don't care since we are already past it. - */ - smp_mb(); - INIT_LIST_HEAD(&epi->rdllink); - } + (revents & epi->event.events)) + list_add_tail(&epi->rdllink, &ep->rdllist); } error = 0; - errxit: +errxit: + write_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 + * here (in case they are not already queued, or they're one-shot). + */ + for (nepi = ep->ovflist; (epi = nepi) != NULL; + nepi = epi->next, epi->next = EP_UNACTIVE_PTR) { + if (!ep_is_linked(&epi->rdllink) && + (epi->event.events & ~EP_PRIVATE_BITS)) + list_add_tail(&epi->rdllink, &ep->rdllist); + } /* - * If the re-injection list or the txlist are not empty, re-splice - * them to the ready list and do proper wakeups. + * 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. */ - if (!list_empty(&injlist) || !list_empty(txlist)) { - write_lock_irqsave(&ep->lock, flags); + ep->ovflist = EP_UNACTIVE_PTR; - list_splice(txlist, &ep->rdllist); - list_splice(&injlist, &ep->rdllist); + /* + * In case of error in the event-send loop, we might still have items + * inside the "txlist". We need to splice them 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() + * Wake up (if active) both the eventpoll wait list and the ->poll() * wait list. */ if (waitqueue_active(&ep->wq)) @@ -1020,9 +1063,10 @@ static int ep_send_events(struct eventpoll *ep, struct list_head *txlist, TASK_INTERRUPTIBLE); if (waitqueue_active(&ep->poll_wait)) pwake++; - - write_unlock_irqrestore(&ep->lock, flags); } + write_unlock_irqrestore(&ep->lock, flags); + + mutex_unlock(&ep->mtx); /* We have to call this outside the lock */ if (pwake) @@ -1031,41 +1075,6 @@ static int ep_send_events(struct eventpoll *ep, struct list_head *txlist, return eventcnt == 0 ? error: eventcnt; } -/* - * Perform the transfer of events to user space. - */ -static int ep_events_transfer(struct eventpoll *ep, - struct epoll_event __user *events, int maxevents) -{ - int eventcnt; - unsigned long flags; - 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). - */ - down_read(&ep->sem); - - /* - * Steal the ready list, and re-init the original one to the - * empty list. - */ - write_lock_irqsave(&ep->lock, flags); - list_splice(&ep->rdllist, &txlist); - INIT_LIST_HEAD(&ep->rdllist); - write_unlock_irqrestore(&ep->lock, flags); - - /* Build result set in userspace */ - eventcnt = ep_send_events(ep, &txlist, events, maxevents); - - up_read(&ep->sem); - - return eventcnt; -} - static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, int maxevents, long timeout) { @@ -1093,6 +1102,7 @@ retry: * 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 (;;) { @@ -1129,7 +1139,7 @@ retry: * more luck. */ if (!res && eavail && - !(res = ep_events_transfer(ep, events, maxevents)) && jtimeout) + !(res = ep_send_events(ep, events, maxevents)) && jtimeout) goto retry; return res; @@ -1237,7 +1247,7 @@ asmlinkage long sys_epoll_ctl(int epfd, int op, int fd, */ ep = file->private_data; - down_write(&ep->sem); + mutex_lock(&ep->mtx); /* Try to lookup the file inside our RB tree */ epi = ep_find(ep, tfile, fd); @@ -1272,7 +1282,7 @@ asmlinkage long sys_epoll_ctl(int epfd, int op, int fd, */ if (epi) ep_release_epitem(epi); - up_write(&ep->sem); + mutex_unlock(&ep->mtx); error_tgt_fput: fput(tfile); |