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Date:   Tue, 1 Oct 2019 09:19:21 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     John Stultz <john.stultz@linaro.org>
Cc:     Ingo Molnar <mingo@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Joel Fernandes <joelaf@google.com>,
        Alistair Delva <adelva@google.com>
Subject: Re: [GIT PULL] scheduler fixes
Message-ID: <20191001071921.GJ4519@hirez.programming.kicks-ass.net>
References: <20190928123905.GA97048@gmail.com>
 <CANcMJZB9UrMaJv6OiScZy2e2UFGFOJsFRar9RZUE9HM-00ZXGg@mail.gmail.com>
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On Mon, Sep 30, 2019 at 04:45:49PM -0700, John Stultz wrote:
> Reverting the following patches:

>   "sched/membarrier: Fix p->mm->membarrier_state racy load"

ARGH, I fudged it... please try:


diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
index a39bed2c784f..168479a7d61b 100644
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -174,7 +174,6 @@ static int membarrier_private_expedited(int flags)
 		 */
 		if (cpu == raw_smp_processor_id())
 			continue;
-		rcu_read_lock();
 		p = rcu_dereference(cpu_rq(cpu)->curr);
 		if (p && p->mm == mm)
 			__cpumask_set_cpu(cpu, tmpmask);