diff options
| -rw-r--r-- | fs/eventpoll.c | 48 |
1 files changed, 27 insertions, 21 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 4c16127..d4255be 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -134,7 +134,7 @@ struct poll_safewake { * 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 */ + /* 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 */ @@ -191,7 +191,7 @@ struct eventpoll { /* List of ready file descriptors */ struct list_head rdllist; - /* RB-Tree root used to store monitored fd structs */ + /* RB tree root used to store monitored fd structs */ struct rb_root rbr; /* @@ -241,7 +241,7 @@ static struct kmem_cache *epi_cache __read_mostly; static struct kmem_cache *pwq_cache __read_mostly; -/* Setup the structure that is used as key for the rb-tree */ +/* 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) { @@ -249,7 +249,7 @@ static inline void ep_set_ffd(struct epoll_filefd *ffd, ffd->fd = fd; } -/* Compare rb-tree keys */ +/* Compare RB tree keys */ static inline int ep_cmp_ffd(struct epoll_filefd *p1, struct epoll_filefd *p2) { @@ -257,20 +257,20 @@ static inline int ep_cmp_ffd(struct epoll_filefd *p1, (p1->file < p2->file ? -1 : p1->fd - p2->fd)); } -/* Special initialization for the rb-tree node to detect linkage */ +/* Special initialization for the RB tree node to detect linkage */ static inline void ep_rb_initnode(struct rb_node *n) { rb_set_parent(n, n); } -/* Removes a node from the rb-tree and marks it for a fast is-linked check */ +/* Removes a node from the RB tree and marks it for a fast is-linked check */ static inline void ep_rb_erase(struct rb_node *n, struct rb_root *r) { rb_erase(n, r); rb_set_parent(n, n); } -/* Fast check to verify that the item is linked to the main rb-tree */ +/* Fast check to verify that the item is linked to the main RB tree */ static inline int ep_rb_linked(struct rb_node *n) { return rb_parent(n) != n; @@ -531,6 +531,8 @@ 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. + * 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 @@ -802,7 +804,9 @@ error_unregister: /* * We need to do this because an event could have been arrived on some - * allocated wait queue. + * 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)) @@ -845,8 +849,7 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even /* * If the item is "hot" and it is not registered inside the ready - * list, push it inside. If the item is not "hot" and it is currently - * registered inside the ready list, unlink it. + * list, push it inside. */ if (revents & event->events) { if (!ep_is_linked(&epi->rdllink)) { @@ -966,15 +969,16 @@ errxit: ep->ovflist = EP_UNACTIVE_PTR; /* - * 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. + * 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. + * wait list (delayed after we release the lock). */ if (waitqueue_active(&ep->wq)) __wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE | @@ -1064,11 +1068,10 @@ retry: } /* - * It opens an eventpoll file descriptor by suggesting a storage of "size" - * file descriptors. The size parameter is just an hint about how to size - * data structures. It won't prevent the user to store more than "size" - * file descriptors inside the epoll interface. It is the kernel part of - * the userspace epoll_create(2). + * It opens an eventpoll file descriptor. The "size" parameter is there + * for historical reasons, when epoll was using an hash instead of an + * RB tree. With the current implementation, the "size" parameter is ignored + * (besides sanity checks). */ asmlinkage long sys_epoll_create(int size) { @@ -1114,8 +1117,7 @@ error_return: /* * The following function implements the controller interface for * the eventpoll file that enables the insertion/removal/change of - * file descriptors inside the interest set. It represents - * the kernel part of the user space epoll_ctl(2). + * file descriptors inside the interest set. */ asmlinkage long sys_epoll_ctl(int epfd, int op, int fd, struct epoll_event __user *event) @@ -1167,7 +1169,11 @@ asmlinkage long sys_epoll_ctl(int epfd, int op, int fd, mutex_lock(&ep->mtx); - /* Try to lookup the file inside our RB tree */ + /* + * 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; |
