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From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@kernel.org>, Thomas Gleixner <tglx@linutronix.de>
Cc: Valentin Schneider <valentin.schneider@arm.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Mel Gorman <mgorman@suse.de>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	linux-kernel@vger.kernel.org, peterz@infradead.org,
	Andi Kleen <andi@firstfloor.org>
Subject: [PATCH 0/6] sched: Fix affine_move_task() wreckage
Date: Wed, 24 Feb 2021 13:24:39 +0100	[thread overview]
Message-ID: <20210224122439.176543586@infradead.org> (raw)

Hi!

The long and short of it is that commit 6d337eab041d ("sched: Fix
migrate_disable() vs set_cpus_allowed_ptr()") is utterly wrecked and it is a
miracle it doesn't insta explode for anybody (else).

The longer story is that after some initial confusion and tracing I found the
first problem and send (patch #1):

  https://lkml.kernel.org/r/YCfLHxpL+L0BYEyG@hirez.programming.kicks-ass.net

and was hoping that was the end of it (ha!). Obviously the one machine that did
manage to trigger this instantly found the next problem, now addressed in patch
#5.

The even longer story is that Monday last I sat down with a large piece of
(virtual) paper, basically threw the entire affine_move_task() /
migration_cpu_stop() logic out and while doodling re-implemented it all.

The difficult machine was happy on the second try after that.

Ofcourse, at that point I had a single huge rewrite of commit 6d337eab041d, and
I pondered sending it like that. However I figured that for review and
posterity it might be easier/better to do smaller steps. So today I reverse
engineerd a possible logical path between the two states.

I'm hoping nothing got wrecked while doing the cleanups :-)

Patches also in:

  git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git sched/urgent



             reply	other threads:[~2021-02-24 14:32 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-24 12:24 Peter Zijlstra [this message]
2021-02-24 12:24 ` [PATCH 1/6] sched: Fix migration_cpu_stop() requeueing Peter Zijlstra
2021-03-01 10:16   ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-03-06 11:42   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-02-24 12:24 ` [PATCH 2/6] sched: Simplify migration_cpu_stop() Peter Zijlstra
2021-02-24 15:34   ` Valentin Schneider
2021-02-25  8:45     ` Peter Zijlstra
2021-02-25 11:10       ` Valentin Schneider
2021-03-01 10:16   ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-03-06 11:42   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-02-24 12:24 ` [PATCH 3/6] sched: Collate affine_move_task() stoppers Peter Zijlstra
2021-03-01 10:16   ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-03-06 11:42   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-02-24 12:24 ` [PATCH 4/6] sched: Optimize migration_cpu_stop() Peter Zijlstra
2021-03-01 10:16   ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-03-06 11:42   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-02-24 12:24 ` [PATCH 5/6] sched: Fix affine_move_task() self-concurrency Peter Zijlstra
2021-03-01 10:16   ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-03-06 11:42   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-02-24 12:24 ` [PATCH 6/6] sched: Simplify set_affinity_pending refcounts Peter Zijlstra
2021-02-24 15:34   ` Valentin Schneider
2021-02-24 15:34   ` Peter Zijlstra
2021-02-24 17:59     ` Valentin Schneider
2021-02-25  9:27       ` Peter Zijlstra
2021-02-25 11:11         ` Valentin Schneider
2021-03-01 10:16   ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-03-06 11:42   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra

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