linux-kernel - [PATCH] sched: Fix 32bit race

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Message-ID: <1310472434.14978.27.camel@twins>
Date:	Tue, 12 Jul 2011 14:07:14 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Mike Galbraith <efault@....de>, bruno <bruno@...ff.to>
Subject: [PATCH] sched: Fix 32bit race

Ingo, can we get the below patch into sched/urgent and towards Linus
before he cuts a release?

I'm surprised there weren't more 32bit-smp doesn't boot for me
complaints, either Bruno is a very 'lucky' man, or nobody is using 32bit
kernels any more since he was hitting this quite reliably.

---
Subject: sched: Fix 32bit race
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Date: Mon Jul 11 16:28:50 CEST 2011

Commit 3fe1698b7fe0 ("sched: Deal with non-atomic min_vruntime reads
on 32bit") forgot to initialize min_vruntime_copy which could lead to
an infinite while loop in task_waking_fair() under some circumstances
(early boot, lucky timing).

Reported-and-tested-by: Bruno Wolff III <bruno@...ff.to>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -7750,6 +7750,9 @@ static void init_cfs_rq(struct cfs_rq *c
 #endif
 #endif
 	cfs_rq->min_vruntime = (u64)(-(1LL << 20));
+#ifndef CONFIG_64BIT
+	cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime;
+#endif
 }
 
 static void init_rt_rq(struct rt_rq *rt_rq, struct rq *rq)

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