epoll: switch epitem->pwqlist to single-linked list

We only traverse it once to destroy all associated eppoll_entry at
epitem destruction time.  The order of traversal is irrelevant there.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 4df61129566d40a21f7016b0900565cdaf68f463..ae41868d9b35c7fef18e26e9c3198061bdc02d35 100644 (file)
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -128,6 +128,24 @@ struct nested_calls {
        spinlock_t lock;
 };
 
+/* Wait structure used by the poll hooks */
+struct eppoll_entry {
+       /* List header used to link this structure to the "struct epitem" */
+       struct eppoll_entry *next;
+
+       /* 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_entry_t wait;
+
+       /* The wait queue head that linked the "wait" wait queue item */
+       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.
@@ -158,7 +176,7 @@ struct epitem {
        int nwait;
 
        /* List containing poll wait queues */
-       struct list_head pwqlist;
+       struct eppoll_entry *pwqlist;
 
        /* The "container" of this item */
        struct eventpoll *ep;
@@ -231,24 +249,6 @@ struct eventpoll {
 #endif
 };
 
-/* 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_entry_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;
@@ -617,13 +617,11 @@ static void ep_remove_wait_queue(struct eppoll_entry *pwq)
  */
 static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
 {
-       struct list_head *lsthead = &epi->pwqlist;
+       struct eppoll_entry **p = &epi->pwqlist;
        struct eppoll_entry *pwq;
 
-       while (!list_empty(lsthead)) {
-               pwq = list_first_entry(lsthead, struct eppoll_entry, llink);
-
-               list_del(&pwq->llink);
+       while ((pwq = *p) != NULL) {
+               *p = pwq->next;
                ep_remove_wait_queue(pwq);
                kmem_cache_free(pwq_cache, pwq);
        }
@@ -1320,7 +1318,8 @@ static void ep_ptable_queue_proc(struct file *file, wait_queue_head_t *whead,
                        add_wait_queue_exclusive(whead, &pwq->wait);
                else
                        add_wait_queue(whead, &pwq->wait);
-               list_add_tail(&pwq->llink, &epi->pwqlist);
+               pwq->next = epi->pwqlist;
+               epi->pwqlist = pwq;
                epi->nwait++;
        } else {
                /* We have to signal that an error occurred */
@@ -1507,7 +1506,7 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
        /* Item initialization follow here ... */
        INIT_LIST_HEAD(&epi->rdllink);
        INIT_LIST_HEAD(&epi->fllink);
-       INIT_LIST_HEAD(&epi->pwqlist);
+       epi->pwqlist = NULL;
        epi->ep = ep;
        ep_set_ffd(&epi->ffd, tfile, fd);
        epi->event = *event;