[RFC PATCH 02/27] epoll: get rid of epitem->nwait

[Al Viro]

From: Al Viro <v...@zeniv.linux.org.uk>

we use it only to indicate allocation failures within queueing
callback back to ep_insert().  Might as well use epq.epi for that
reporting...

Signed-off-by: Al Viro <v...@zeniv.linux.org.uk>
---
 fs/eventpoll.c | 46 ++++++++++++++++++++--------------------------
 1 file changed, 20 insertions(+), 26 deletions(-)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index ae41868d9b35..44aca681d897 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -172,9 +172,6 @@ struct epitem {
        /* 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 eppoll_entry *pwqlist;
 
@@ -351,12 +348,6 @@ static inline struct epitem 
*ep_item_from_wait(wait_queue_entry_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;
-}
-
 /* Initialize the poll safe wake up structure */
 static void ep_nested_calls_init(struct nested_calls *ncalls)
 {
@@ -1307,24 +1298,28 @@ static int ep_poll_callback(wait_queue_entry_t *wait, 
unsigned mode, int sync, v
 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 ep_pqueue *epq = container_of(pt, struct ep_pqueue, pt);
+       struct epitem *epi = epq->epi;
        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;
-               if (epi->event.events & EPOLLEXCLUSIVE)
-                       add_wait_queue_exclusive(whead, &pwq->wait);
-               else
-                       add_wait_queue(whead, &pwq->wait);
-               pwq->next = epi->pwqlist;
-               epi->pwqlist = pwq;
-               epi->nwait++;
-       } else {
-               /* We have to signal that an error occurred */
-               epi->nwait = -1;
+       if (unlikely(!epi))     // an earlier allocation has failed
+               return;
+
+       pwq = kmem_cache_alloc(pwq_cache, GFP_KERNEL);
+       if (unlikely(!pwq)) {
+               epq->epi = NULL;
+               return;
        }
+
+       init_waitqueue_func_entry(&pwq->wait, ep_poll_callback);
+       pwq->whead = whead;
+       pwq->base = epi;
+       if (epi->event.events & EPOLLEXCLUSIVE)
+               add_wait_queue_exclusive(whead, &pwq->wait);
+       else
+               add_wait_queue(whead, &pwq->wait);
+       pwq->next = epi->pwqlist;
+       epi->pwqlist = pwq;
 }
 
 static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
@@ -1510,7 +1505,6 @@ static int ep_insert(struct eventpoll *ep, const struct 
epoll_event *event,
        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);
@@ -1555,7 +1549,7 @@ static int ep_insert(struct eventpoll *ep, const struct 
epoll_event *event,
         * high memory pressure.
         */
        error = -ENOMEM;
-       if (epi->nwait < 0)
+       if (!epq.epi)
                goto error_unregister;
 
        /* We have to drop the new item inside our item list to keep track of 
it */
-- 
2.11.0