linux-kernel - [patch -rt] Fix infinite loop with 2.6.31.4-rt14 V2

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Message-ID: <20091023200858.GA7011@in.ibm.com>
Date:	Sat, 24 Oct 2009 01:38:58 +0530
From:	Dinakar Guniguntala <dino@...ibm.com>
To:	Darren Hart <dvhltc@...ibm.com>
Cc:	tglx@...utronix.de, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org
Subject: [patch -rt] Fix infinite loop with 2.6.31.4-rt14 V2


Application threads calling futex_wait_requeue_pi run in an infinite loop
in the kernel if the futex value changes during the call. The following
patch fixes the problem.

Signed-off-by: Dinakar Guniguntala <dino@...ibm.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Darren Hart <dvhltc@...ibm.com>

---
 kernel/futex.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

Index: linux-2.6.31.4-rt14-lbf-f1/kernel/futex.c
===================================================================
--- linux-2.6.31.4-rt14-lbf-f1.orig/kernel/futex.c
+++ linux-2.6.31.4-rt14-lbf-f1/kernel/futex.c
@@ -2188,6 +2188,12 @@ retry:
 	spin_lock(&hb->lock);
 	ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
 	spin_unlock(&hb->lock);
+	if (ret == -EAGAIN) {
+		/* Retry on spurious wakeup */
+		put_futex_key(fshared, &q.key);
+		put_futex_key(fshared, &key2);
+		goto retry;
+	}
 	if (ret)
 		goto out_put_keys;
 
@@ -2264,9 +2270,6 @@ out_put_keys:
 out_key2:
 	put_futex_key(fshared, &key2);
 
-	/* Spurious wakeup ? */
-	if (ret == -EAGAIN)
-		goto retry;
 out:
 	if (to) {
 		hrtimer_cancel(&to->timer);
--
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