[PATCH] 2.5.46: epoll ep_insert doesn't wake waiters if events exist

["Jay Vosburgh" <fubar@us.ibm.com>]

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      The logic in fs/eventpoll.c:ep_insert()  checks to see if events are
already present when processing an EP_CTL_ADD operation, and, if any are,
adds them to the list.  It does not wake up any waiters, so, e.g., another
thread waiting in epoll_wait() will not be awakened for these events.  The
fix is to have ep_insert() do wakeups, just as ep_poll_callback() does when
it adds events.

      -J

diff -ur linux-2.5.46.orig/fs/eventpoll.c linux-2.5.46/fs/eventpoll.c
--- linux-2.5.46.orig/fs/eventpoll.c      Thu Nov  7 14:31:21 2002
+++ linux-2.5.46/fs/eventpoll.c     Thu Nov  7 14:32:16 2002
@@ -838,8 +838,13 @@
      list_add(&dpi->llink, ep_hash_entry(ep, ep_hash_index(ep, tfile)));

      /* If the file is already "ready" we drop it inside the ready list */
-     if ((revents & pfd->events) && !EP_IS_LINKED(&dpi->rdllink))
+     if ((revents & pfd->events) && !EP_IS_LINKED(&dpi->rdllink)) {
            list_add(&dpi->rdllink, &ep->rdllist);
+           if (waitqueue_active(&ep->wq))
+                 wake_up(&ep->wq);
+           if (waitqueue_active(&ep->poll_wait))
+                 wake_up(&ep->poll_wait);
+     }

      write_unlock_irqrestore(&ep->lock, flags);



(See attached file: epoll-2.5.46-insert.patch)

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diff -ur linux-2.5.46.orig/fs/eventpoll.c linux-2.5.46/fs/eventpoll.c
--- linux-2.5.46.orig/fs/eventpoll.c	Thu Nov  7 14:31:21 2002
+++ linux-2.5.46/fs/eventpoll.c	Thu Nov  7 14:32:16 2002
@@ -838,8 +838,13 @@
 	list_add(&dpi->llink, ep_hash_entry(ep, ep_hash_index(ep, tfile)));
 
 	/* If the file is already "ready" we drop it inside the ready list */
-	if ((revents & pfd->events) && !EP_IS_LINKED(&dpi->rdllink))
+	if ((revents & pfd->events) && !EP_IS_LINKED(&dpi->rdllink)) {
 		list_add(&dpi->rdllink, &ep->rdllist);
+		if (waitqueue_active(&ep->wq))
+			wake_up(&ep->wq);
+		if (waitqueue_active(&ep->poll_wait))
+			wake_up(&ep->poll_wait);
+	}
 
 	write_unlock_irqrestore(&ep->lock, flags);