linux-kernel - Re: [tip: sched/core] sched: Replace rq::wake

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Date:   Tue, 2 Jun 2020 17:16:07 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     linux-tip-commits@...r.kernel.org,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, x86 <x86@...nel.org>
Subject: Re: [tip: sched/core] sched: Replace rq::wake_list

On Mon, Jun 01, 2020 at 09:52:18AM -0000, tip-bot2 for Peter Zijlstra wrote:
> The following commit has been merged into the sched/core branch of tip:
> 
> Commit-ID:     a148866489fbe243c936fe43e4525d8dbfa0318f
> Gitweb:        https://git.kernel.org/tip/a148866489fbe243c936fe43e4525d8dbfa0318f
> Author:        Peter Zijlstra <peterz@...radead.org>
> AuthorDate:    Tue, 26 May 2020 18:11:04 +02:00
> Committer:     Ingo Molnar <mingo@...nel.org>
> CommitterDate: Thu, 28 May 2020 10:54:16 +02:00
> 
> sched: Replace rq::wake_list
> 
> The recent commit: 90b5363acd47 ("sched: Clean up scheduler_ipi()")
> got smp_call_function_single_async() subtly wrong. Even though it will
> return -EBUSY when trying to re-use a csd, that condition is not
> atomic and still requires external serialization.
> 
> The change in ttwu_queue_remote() got this wrong.
> 
> While on first reading ttwu_queue_remote() has an atomic test-and-set
> that appears to serialize the use, the matching 'release' is not in
> the right place to actually guarantee this serialization.
> 
> The actual race is vs the sched_ttwu_pending() call in the idle loop;
> that can run the wakeup-list without consuming the CSD.
> 
> Instead of trying to chain the lists, merge them.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> Link: https://lore.kernel.org/r/20200526161908.129371594@infradead.org

Looks good, thanks :)