epoll: support for disabling items, and a self-test app
Enhanced epoll_ctl to support EPOLL_CTL_DISABLE, which disables an epoll
item. If epoll_ctl doesn't return -EBUSY in this case, it is then safe to
delete the epoll item in a multi-threaded environment. Also added a new
test_epoll self- test app to both demonstrate the need for this feature
and test it.
Signed-off-by: Paton J. Lewis <palewis@adobe.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jason Baron <jbaron@redhat.com>
Cc: Paul Holland <pholland@adobe.com>
Cc: Davide Libenzi <davidel@xmailserver.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index cd96649..da72250 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -346,7 +346,7 @@
/* Tells if the epoll_ctl(2) operation needs an event copy from userspace */
static inline int ep_op_has_event(int op)
{
- return op != EPOLL_CTL_DEL;
+ return op == EPOLL_CTL_ADD || op == EPOLL_CTL_MOD;
}
/* Initialize the poll safe wake up structure */
@@ -676,6 +676,34 @@
return 0;
}
+/*
+ * Disables a "struct epitem" in the eventpoll set. Returns -EBUSY if the item
+ * had no event flags set, indicating that another thread may be currently
+ * handling that item's events (in the case that EPOLLONESHOT was being
+ * used). Otherwise a zero result indicates that the item has been disabled
+ * from receiving events. A disabled item may be re-enabled via
+ * EPOLL_CTL_MOD. Must be called with "mtx" held.
+ */
+static int ep_disable(struct eventpoll *ep, struct epitem *epi)
+{
+ int result = 0;
+ unsigned long flags;
+
+ spin_lock_irqsave(&ep->lock, flags);
+ if (epi->event.events & ~EP_PRIVATE_BITS) {
+ if (ep_is_linked(&epi->rdllink))
+ list_del_init(&epi->rdllink);
+ /* Ensure ep_poll_callback will not add epi back onto ready
+ list: */
+ epi->event.events &= EP_PRIVATE_BITS;
+ }
+ else
+ result = -EBUSY;
+ spin_unlock_irqrestore(&ep->lock, flags);
+
+ return result;
+}
+
static void ep_free(struct eventpoll *ep)
{
struct rb_node *rbp;
@@ -1020,8 +1048,6 @@
rb_insert_color(&epi->rbn, &ep->rbr);
}
-
-
#define PATH_ARR_SIZE 5
/*
* These are the number paths of length 1 to 5, that we are allowing to emanate
@@ -1787,6 +1813,12 @@
} else
error = -ENOENT;
break;
+ case EPOLL_CTL_DISABLE:
+ if (epi)
+ error = ep_disable(ep, epi);
+ else
+ error = -ENOENT;
+ break;
}
mutex_unlock(&ep->mtx);