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@@ -26,7 +26,6 @@
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#include <linux/hash.h>
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#include <linux/spinlock.h>
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#include <linux/syscalls.h>
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-#include <linux/rwsem.h>
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#include <linux/rbtree.h>
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#include <linux/wait.h>
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#include <linux/eventpoll.h>
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@@ -39,14 +38,13 @@
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#include <asm/io.h>
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#include <asm/mman.h>
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#include <asm/atomic.h>
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-#include <asm/semaphore.h>
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/*
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* LOCKING:
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* There are three level of locking required by epoll :
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*
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* 1) epmutex (mutex)
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- * 2) ep->sem (rw_semaphore)
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+ * 2) ep->mtx (mutes)
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* 3) ep->lock (rw_lock)
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*
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* The acquire order is the one listed above, from 1 to 3.
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@@ -57,20 +55,20 @@
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* a spinlock. During the event transfer loop (from kernel to
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* user space) we could end up sleeping due a copy_to_user(), so
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* we need a lock that will allow us to sleep. This lock is a
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- * read-write semaphore (ep->sem). It is acquired on read during
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- * the event transfer loop and in write during epoll_ctl(EPOLL_CTL_DEL)
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- * and during eventpoll_release_file(). Then we also need a global
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- * semaphore to serialize eventpoll_release_file() and ep_free().
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- * This semaphore is acquired by ep_free() during the epoll file
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+ * mutex (ep->mtx). It is acquired during the event transfer loop,
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+ * during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file().
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+ * Then we also need a global mutex to serialize eventpoll_release_file()
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+ * and ep_free().
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+ * This mutex is acquired by ep_free() during the epoll file
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* cleanup path and it is also acquired by eventpoll_release_file()
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* if a file has been pushed inside an epoll set and it is then
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* close()d without a previous call toepoll_ctl(EPOLL_CTL_DEL).
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- * It is possible to drop the "ep->sem" and to use the global
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- * semaphore "epmutex" (together with "ep->lock") to have it working,
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- * but having "ep->sem" will make the interface more scalable.
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+ * It is possible to drop the "ep->mtx" and to use the global
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+ * mutex "epmutex" (together with "ep->lock") to have it working,
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+ * but having "ep->mtx" will make the interface more scalable.
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* Events that require holding "epmutex" are very rare, while for
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- * normal operations the epoll private "ep->sem" will guarantee
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- * a greater scalability.
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+ * normal operations the epoll private "ep->mtx" will guarantee
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+ * a better scalability.
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*/
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#define DEBUG_EPOLL 0
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@@ -102,6 +100,8 @@
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#define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))
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+#define EP_UNACTIVE_PTR ((void *) -1L)
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+
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struct epoll_filefd {
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struct file *file;
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int fd;
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@@ -111,7 +111,7 @@ struct epoll_filefd {
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* Node that is linked into the "wake_task_list" member of the "struct poll_safewake".
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* It is used to keep track on all tasks that are currently inside the wake_up() code
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* to 1) short-circuit the one coming from the same task and same wait queue head
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- * ( loop ) 2) allow a maximum number of epoll descriptors inclusion nesting
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+ * (loop) 2) allow a maximum number of epoll descriptors inclusion nesting
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* 3) let go the ones coming from other tasks.
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*/
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struct wake_task_node {
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@@ -129,6 +129,48 @@ struct poll_safewake {
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spinlock_t lock;
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};
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+/*
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+ * Each file descriptor added to the eventpoll interface will
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+ * have an entry of this type linked to the "rbr" RB tree.
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+ */
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+struct epitem {
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+ /* RB-Tree node used to link this structure to the eventpoll rb-tree */
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+ struct rb_node rbn;
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+
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+ /* List header used to link this structure to the eventpoll ready list */
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+ struct list_head rdllink;
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+
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+ /* The file descriptor information this item refers to */
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+ struct epoll_filefd ffd;
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+
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+ /* Number of active wait queue attached to poll operations */
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+ int nwait;
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+
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+ /* List containing poll wait queues */
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+ struct list_head pwqlist;
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+
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+ /* The "container" of this item */
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+ struct eventpoll *ep;
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+
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+ /* The structure that describe the interested events and the source fd */
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+ struct epoll_event event;
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+
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+ /*
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+ * Used to keep track of the usage count of the structure. This avoids
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+ * that the structure will desappear from underneath our processing.
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+ */
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+ atomic_t usecnt;
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+
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+ /* List header used to link this item to the "struct file" items list */
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+ struct list_head fllink;
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+
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+ /*
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+ * Works together "struct eventpoll"->ovflist in keeping the
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+ * single linked chain of items.
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+ */
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+ struct epitem *next;
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+};
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+
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/*
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* This structure is stored inside the "private_data" member of the file
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* structure and rapresent the main data sructure for the eventpoll
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@@ -139,12 +181,12 @@ struct eventpoll {
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rwlock_t lock;
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/*
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- * This semaphore is used to ensure that files are not removed
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- * while epoll is using them. This is read-held during the event
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- * collection loop and it is write-held during the file cleanup
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- * path, the epoll file exit code and the ctl operations.
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+ * This mutex is used to ensure that files are not removed
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+ * while epoll is using them. This is held during the event
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+ * collection loop, the file cleanup path, the epoll file exit
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+ * code and the ctl operations.
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*/
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- struct rw_semaphore sem;
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+ struct mutex mtx;
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/* Wait queue used by sys_epoll_wait() */
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wait_queue_head_t wq;
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@@ -157,6 +199,13 @@ struct eventpoll {
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/* RB-Tree root used to store monitored fd structs */
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struct rb_root rbr;
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+
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+ /*
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+ * This is a single linked list that chains all the "struct epitem" that
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+ * happened while transfering ready events to userspace w/out
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+ * holding ->lock.
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+ */
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+ struct epitem *ovflist;
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};
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/* Wait structure used by the poll hooks */
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@@ -177,42 +226,6 @@ struct eppoll_entry {
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wait_queue_head_t *whead;
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};
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-/*
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- * Each file descriptor added to the eventpoll interface will
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- * have an entry of this type linked to the "rbr" RB tree.
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- */
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-struct epitem {
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- /* RB-Tree node used to link this structure to the eventpoll rb-tree */
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- struct rb_node rbn;
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-
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- /* List header used to link this structure to the eventpoll ready list */
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- struct list_head rdllink;
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-
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- /* The file descriptor information this item refers to */
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- struct epoll_filefd ffd;
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-
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- /* Number of active wait queue attached to poll operations */
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- int nwait;
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-
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- /* List containing poll wait queues */
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- struct list_head pwqlist;
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-
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- /* The "container" of this item */
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- struct eventpoll *ep;
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-
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- /* The structure that describe the interested events and the source fd */
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- struct epoll_event event;
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-
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- /*
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- * Used to keep track of the usage count of the structure. This avoids
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- * that the structure will desappear from underneath our processing.
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- */
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- atomic_t usecnt;
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-
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- /* List header used to link this item to the "struct file" items list */
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- struct list_head fllink;
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-};
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-
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/* Wrapper struct used by poll queueing */
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struct ep_pqueue {
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poll_table pt;
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@@ -220,7 +233,7 @@ struct ep_pqueue {
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};
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/*
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- * This semaphore is used to serialize ep_free() and eventpoll_release_file().
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+ * This mutex is used to serialize ep_free() and eventpoll_release_file().
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*/
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static struct mutex epmutex;
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@@ -506,7 +519,7 @@ static void ep_free(struct eventpoll *ep)
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/*
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* We need to lock this because we could be hit by
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* eventpoll_release_file() while we're freeing the "struct eventpoll".
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- * We do not need to hold "ep->sem" here because the epoll file
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+ * We do not need to hold "ep->mtx" here because the epoll file
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* is on the way to be removed and no one has references to it
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* anymore. The only hit might come from eventpoll_release_file() but
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* holding "epmutex" is sufficent here.
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@@ -525,7 +538,7 @@ static void ep_free(struct eventpoll *ep)
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/*
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* Walks through the whole tree by freeing each "struct epitem". At this
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* point we are sure no poll callbacks will be lingering around, and also by
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- * write-holding "sem" we can be sure that no file cleanup code will hit
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+ * holding "epmutex" we can be sure that no file cleanup code will hit
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* us during this operation. So we can avoid the lock on "ep->lock".
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*/
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while ((rbp = rb_first(&ep->rbr)) != 0) {
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@@ -534,6 +547,8 @@ static void ep_free(struct eventpoll *ep)
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}
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mutex_unlock(&epmutex);
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+
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+ mutex_destroy(&ep->mtx);
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}
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static int ep_eventpoll_release(struct inode *inode, struct file *file)
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@@ -594,9 +609,9 @@ void eventpoll_release_file(struct file *file)
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* We don't want to get "file->f_ep_lock" because it is not
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* necessary. It is not necessary because we're in the "struct file"
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* cleanup path, and this means that noone is using this file anymore.
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- * The only hit might come from ep_free() but by holding the semaphore
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+ * The only hit might come from ep_free() but by holding the mutex
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* will correctly serialize the operation. We do need to acquire
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- * "ep->sem" after "epmutex" because ep_remove() requires it when called
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+ * "ep->mtx" after "epmutex" because ep_remove() requires it when called
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* from anywhere but ep_free().
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*/
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mutex_lock(&epmutex);
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@@ -606,9 +621,9 @@ void eventpoll_release_file(struct file *file)
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ep = epi->ep;
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list_del_init(&epi->fllink);
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- down_write(&ep->sem);
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+ mutex_lock(&ep->mtx);
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ep_remove(ep, epi);
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- up_write(&ep->sem);
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+ mutex_unlock(&ep->mtx);
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}
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mutex_unlock(&epmutex);
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@@ -622,11 +637,12 @@ static int ep_alloc(struct eventpoll **pep)
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return -ENOMEM;
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rwlock_init(&ep->lock);
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- init_rwsem(&ep->sem);
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+ mutex_init(&ep->mtx);
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init_waitqueue_head(&ep->wq);
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init_waitqueue_head(&ep->poll_wait);
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INIT_LIST_HEAD(&ep->rdllist);
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ep->rbr = RB_ROOT;
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+ ep->ovflist = EP_UNACTIVE_PTR;
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*pep = ep;
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@@ -695,7 +711,21 @@ static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *k
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* until the next EPOLL_CTL_MOD will be issued.
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*/
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if (!(epi->event.events & ~EP_PRIVATE_BITS))
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- goto is_disabled;
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+ goto out_unlock;
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+
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+ /*
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+ * If we are trasfering events to userspace, we can hold no locks
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+ * (because we're accessing user memory, and because of linux f_op->poll()
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+ * semantics). All the events that happens during that period of time are
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+ * chained in ep->ovflist and requeued later on.
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+ */
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+ if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) {
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+ if (epi->next == EP_UNACTIVE_PTR) {
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+ epi->next = ep->ovflist;
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+ ep->ovflist = epi;
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+ }
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+ goto out_unlock;
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+ }
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/* If this file is already in the ready list we exit soon */
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if (ep_is_linked(&epi->rdllink))
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@@ -714,7 +744,7 @@ is_linked:
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if (waitqueue_active(&ep->poll_wait))
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pwake++;
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-is_disabled:
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+out_unlock:
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write_unlock_irqrestore(&ep->lock, flags);
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/* We have to call this outside the lock */
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@@ -788,6 +818,7 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
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epi->event = *event;
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atomic_set(&epi->usecnt, 1);
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epi->nwait = 0;
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+ epi->next = EP_UNACTIVE_PTR;
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/* Initialize the poll table using the queue callback */
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epq.epi = epi;
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@@ -920,36 +951,50 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even
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return 0;
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}
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-/*
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- * This function is called without holding the "ep->lock" since the call to
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- * __copy_to_user() might sleep, and also f_op->poll() might reenable the IRQ
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- * because of the way poll() is traditionally implemented in Linux.
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- */
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-static int ep_send_events(struct eventpoll *ep, struct list_head *txlist,
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- struct epoll_event __user *events, int maxevents)
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+static int ep_send_events(struct eventpoll *ep, struct epoll_event __user *events,
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+ int maxevents)
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{
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int eventcnt, error = -EFAULT, pwake = 0;
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unsigned int revents;
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unsigned long flags;
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- struct epitem *epi;
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- struct list_head injlist;
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+ struct epitem *epi, *nepi;
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+ struct list_head txlist;
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+
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+ INIT_LIST_HEAD(&txlist);
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- INIT_LIST_HEAD(&injlist);
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+ /*
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+ * We need to lock this because we could be hit by
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+ * eventpoll_release_file() and epoll_ctl(EPOLL_CTL_DEL).
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+ */
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+ mutex_lock(&ep->mtx);
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+
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+ /*
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+ * Steal the ready list, and re-init the original one to the
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+ * empty list. Also, set ep->ovflist to NULL so that events
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+ * happening while looping w/out locks, are not lost. We cannot
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+ * have the poll callback to queue directly on ep->rdllist,
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+ * because we are doing it in the loop below, in a lockless way.
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+ */
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+ write_lock_irqsave(&ep->lock, flags);
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+ list_splice(&ep->rdllist, &txlist);
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+ INIT_LIST_HEAD(&ep->rdllist);
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+ ep->ovflist = NULL;
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+ write_unlock_irqrestore(&ep->lock, flags);
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/*
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* We can loop without lock because this is a task private list.
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* We just splice'd out the ep->rdllist in ep_collect_ready_items().
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- * Items cannot vanish during the loop because we are holding "sem" in
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- * read.
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+ * Items cannot vanish during the loop because we are holding "mtx".
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*/
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- for (eventcnt = 0; !list_empty(txlist) && eventcnt < maxevents;) {
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- epi = list_first_entry(txlist, struct epitem, rdllink);
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- prefetch(epi->rdllink.next);
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+ for (eventcnt = 0; !list_empty(&txlist) && eventcnt < maxevents;) {
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+ epi = list_first_entry(&txlist, struct epitem, rdllink);
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+
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+ list_del_init(&epi->rdllink);
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/*
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* Get the ready file event set. We can safely use the file
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- * because we are holding the "sem" in read and this will
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- * guarantee that both the file and the item will not vanish.
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+ * because we are holding the "mtx" and this will guarantee
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+ * that both the file and the item will not vanish.
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*/
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revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);
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revents &= epi->event.events;
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@@ -957,8 +1002,8 @@ static int ep_send_events(struct eventpoll *ep, struct list_head *txlist,
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/*
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* Is the event mask intersect the caller-requested one,
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* deliver the event to userspace. Again, we are holding
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- * "sem" in read, so no operations coming from userspace
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- * can change the item.
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+ * "mtx", so no operations coming from userspace can change
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+ * the item.
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*/
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if (revents) {
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if (__put_user(revents,
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@@ -970,49 +1015,47 @@ static int ep_send_events(struct eventpoll *ep, struct list_head *txlist,
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epi->event.events &= EP_PRIVATE_BITS;
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eventcnt++;
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|
|
}
|
|
|
-
|
|
|
/*
|
|
|
- * 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);
|