linux-kernel - [patch] eventfd/kaio integration fix

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Message-ID: <Pine.LNX.4.64.0804091138050.7000@alien.or.mcafeemobile.com>
Date:	Wed, 9 Apr 2008 11:45:47 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Zach Brown <zach.brown@...cle.com>,
	Jeff Roberson <jroberson@...sapeake.net>
Subject: [patch] eventfd/kaio integration fix

Jeff Roberson discovered a race when using kaio eventfd based 
notifications. 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@...ilserver.org>


- Davide


---
 fs/aio.c |   17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

Index: linux-2.6.mod/fs/aio.c
===================================================================
--- linux-2.6.mod.orig/fs/aio.c	2008-04-08 16:25:27.000000000 -0700
+++ linux-2.6.mod/fs/aio.c	2008-04-09 11:37:10.000000000 -0700
@@ -936,14 +936,6 @@
 		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 @@
 	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);
--
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