linux-kernel - [PATCH -v2] futex: fix reference leak

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Message-Id: <1234205874.5951.151.camel@laptop>
Date:	Mon, 09 Feb 2009 19:57:54 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Darren Hart <dvhltc@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>
Subject: [PATCH -v2] futex: fix reference leak

On Mon, 2009-02-09 at 10:53 -0800, Pallipadi, Venkatesh wrote:
> Yes. This patch fixes the problem on my system. With git, without the
> patch I see the same oops as before on reboot. With the patch, system
> reboots cleanly.
> 
> A minor typo in the patch
> + ret = -RESTART_RESTARTBLOCK;
> should be
> + ret = -ERESTART_RESTARTBLOCK;

Gah, so much for my copy-paste skillz ;-)

Thanks!

---
Catalin noticed that (38d47c1b7075: futex: rely on
get_user_pages() for shared futexes) caused an mm_struct leak.

Some tracing with the function graph tracer quickly pointed out that
futex_wait() has exit paths with unbalanced reference counts.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Tested-by: "Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
---
 kernel/futex.c |   23 +++++++++++++++--------
 1 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index f89d373..ff06c76 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1284,18 +1284,23 @@ retry:
 	 */
 
 	/* If we were woken (and unqueued), we succeeded, whatever. */
-	if (!unqueue_me(&q))
-		return 0;
-	if (rem)
-		return -ETIMEDOUT;
+	if (!unqueue_me(&q)) {
+		ret = 0;
+		goto out_put_key;
+	}
+	if (rem) {
+		ret = -ETIMEDOUT;
+		goto out_put_key;
+	}
 
 	/*
 	 * We expect signal_pending(current), but another thread may
 	 * have handled it for us already.
 	 */
-	if (!abs_time)
-		return -ERESTARTSYS;
-	else {
+	if (!abs_time) {
+		ret = -ERESTARTSYS;
+		goto out_put_key;
+	} else {
 		struct restart_block *restart;
 		restart = &current_thread_info()->restart_block;
 		restart->fn = futex_wait_restart;
@@ -1309,11 +1314,13 @@ retry:
 			restart->futex.flags |= FLAGS_SHARED;
 		if (clockrt)
 			restart->futex.flags |= FLAGS_CLOCKRT;
-		return -ERESTART_RESTARTBLOCK;
+		ret = -ERESTART_RESTARTBLOCK;
+		goto out_put_key;
 	}
 
 out_unlock_put_key:
 	queue_unlock(&q, hb);
+out_put_key:
 	put_futex_key(fshared, &q.key);
 
 out:


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