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Date:   Fri, 11 Oct 2019 09:52:13 -0700
From:   Tejun Heo <tj@kernel.org>
To:     Oleg Nesterov <oleg@redhat.com>
Cc:     linux-kernel@vger.kernel.org, Roman Gushchin <guro@fb.com>,
        Richard Purdie <richard.purdie@linuxfoundation.org>,
        Bruce Ashfield <bruce.ashfield@gmail.com>
Subject: Re: [PATCH] cgroup: freezer: call cgroup_enter_frozen() with
 preemption disabled in ptrace_stop()
Message-ID: <20191011165213.GB18794@devbig004.ftw2.facebook.com>
References: <CADkTA4PBT374CY+UNb85WjQEaNCDodMZu=MgpG8aMYbAu2eOGA@mail.gmail.com>
 <20191009150230.GB12511@redhat.com>
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On Wed, Oct 09, 2019 at 05:02:30PM +0200, Oleg Nesterov wrote:
> ptrace_stop() does preempt_enable_no_resched() to avoid the preemption,
> but after that cgroup_enter_frozen() does spin_lock/unlock and this adds
> another preemption point.
> 
> Reported-and-tested-by: Bruce Ashfield <bruce.ashfield@gmail.com>
> Fixes: 76f969e8948d ("cgroup: cgroup v2 freezer")
> Cc: stable@vger.kernel.org # v5.2+
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Applied to cgroup/for-5.4-fixes.

Thanks.

-- 
tejun