eventfd/kaio integration fix

Jeff Roberson discovered a race when using kaio eventfd based notifications.
When it occurs it can lead tomissed wakeups and hung userspace.

This patch fixes the race by moving the notification inside the spinlocked
section of kaio.  The operation is safe since eventfd spinlock and kaio one
are unrelated.

Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Cc: Zach Brown <zach.brown@oracle.com>
Cc: Jeff Roberson <jroberson@chesapeake.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/aio.c b/fs/aio.c
index 60a4cd4d11376a3688f822d3ce30798717833a19..228368610dfa64e7af06ec9dd864074cf550851e 100644 (file)
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -936,14 +936,6 @@ int aio_complete(struct kiocb *iocb, long res, long res2)
                return 1;
        }
 
-       /*
-        * Check if the user asked us to deliver the result through an
-        * eventfd. The eventfd_signal() function is safe to be called
-        * from IRQ context.
-        */
-       if (!IS_ERR(iocb->ki_eventfd))
-               eventfd_signal(iocb->ki_eventfd, 1);
-
        info = &ctx->ring_info;
 
        /* add a completion event to the ring buffer.
@@ -992,6 +984,15 @@ int aio_complete(struct kiocb *iocb, long res, long res2)
        kunmap_atomic(ring, KM_IRQ1);
 
        pr_debug("added to ring %p at [%lu]\n", iocb, tail);
+
+       /*
+        * Check if the user asked us to deliver the result through an
+        * eventfd. The eventfd_signal() function is safe to be called
+        * from IRQ context.
+        */
+       if (!IS_ERR(iocb->ki_eventfd))
+               eventfd_signal(iocb->ki_eventfd, 1);
+
 put_rq:
        /* everything turned out well, dispose of the aiocb. */
        ret = __aio_put_req(ctx, iocb);