linux-kernel - Re: [STABLE] kernel oops which can be fixed by peterz's patches

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Message-ID: <1456261613.9099.0.camel@decadent.org.uk>
Date:	Tue, 23 Feb 2016 21:06:53 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Mike Galbraith <umgwanakikbuti@...il.com>,
	Byungchul Park <byungchul.park@....com>,
	Greg KH <gregkh@...uxfoundation.org>
Cc:	Peter Zijlstra <peterz@...radead.org>, stable@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [STABLE] kernel oops which can be fixed by peterz's patches

On Wed, 2016-02-17 at 04:02 +0100, Mike Galbraith wrote:
[...]

@stable: Kernels that predate SCHED_DEADLINE can use this simple (and tested)
check in lieu of backport of the full 18 patch mainline treatment.

Signed-off-by: Mike Galbraith <umgwanakikbuti@...il.com>
---
 kernel/sched/fair.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4008,6 +4008,7 @@ int can_migrate_task(struct task_struct
 	 * 2) cannot be migrated to this CPU due to cpus_allowed, or
 	 * 3) running (obviously), or
 	 * 4) are cache-hot on their current CPU.
+	 * 5) p->pi_lock is held.
 	 */
 	if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu))
 		return 0;
@@ -4049,6 +4050,14 @@ int can_migrate_task(struct task_struct
 	}
 
 	/*
+	 * rt -> fair class change may be in progress.  If we sneak in should
+	 * double_lock_balance() release rq->lock, and move the task, we will
+	 * cause switched_to_fair() to meet a passed but no longer valid rq.
+	 */
+	if (raw_spin_is_locked(&p->pi_lock))
+		return 0;
+
+	/*
 	 * Aggressive migration if:
 	 * 1) task is cache cold, or
 	 * 2) too many balance attempts have failed.



Queued up for 3.2, thanks.

Ben.

-- 
Ben Hutchings
Any smoothly functioning technology is indistinguishable from a rigged demo.
-- 
Ben Hutchings
Any smoothly functioning technology is indistinguishable from a rigged demo.

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