linux-kernel - Re: [tip: sched/core] sched: Fix smp_call_function_single

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Message-ID: <20200601114007.GA20995@lenoir>
Date:   Mon, 1 Jun 2020 13:40:08 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>
Cc:     linux-tip-commits@...r.kernel.org, Qian Cai <cai@....pw>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        mgorman@...hsingularity.net, x86 <x86@...nel.org>
Subject: Re: [tip: sched/core] sched: Fix smp_call_function_single_async()
 usage for ILB

On Mon, Jun 01, 2020 at 09:52:21AM -0000, tip-bot2 for Peter Zijlstra wrote:
> The following commit has been merged into the sched/core branch of tip:
> 
> Commit-ID:     19a1f5ec699954d21be10f74ff71c2a7079e99ad
> Gitweb:        https://git.kernel.org/tip/19a1f5ec699954d21be10f74ff71c2a7079e99ad
> Author:        Peter Zijlstra <peterz@...radead.org>
> AuthorDate:    Tue, 26 May 2020 18:10:58 +02:00
> Committer:     Ingo Molnar <mingo@...nel.org>
> CommitterDate: Thu, 28 May 2020 10:54:15 +02:00
> 
> sched: Fix smp_call_function_single_async() usage for ILB
> 
> 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 kick_ilb() got this wrong.
> 
> While on first reading kick_ilb() 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.
> 
> Rework the nohz_idle_balance() trigger so that the release is in the
> IPI callback and thus guarantees the required serialization for the
> CSD.
> 
> Fixes: 90b5363acd47 ("sched: Clean up scheduler_ipi()")
> Reported-by: Qian Cai <cai@....pw>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
> Cc: mgorman@...hsingularity.net
> Link: https://lore.kernel.org/r/20200526161907.778543557@infradead.org

Many patches in the series lack some Reviewed-by tags.

Thanks.