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Date:   Thu, 11 Mar 2021 10:01:22 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Mike Kravetz <mike.kravetz@oracle.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Shakeel Butt <shakeelb@google.com>, tglx@linutronix.de,
        john.ogness@linutronix.de, urezki@gmail.com, ast@fb.com,
        Eric Dumazet <edumazet@google.com>,
        Mina Almasry <almasrymina@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] hugetlb: select PREEMPT_COUNT if HUGETLB_PAGE for
 in_atomic use
Message-ID: <YEncYrWCVn2/20/C@dhcp22.suse.cz>
References: <20210311021321.127500-1-mike.kravetz@oracle.com>
 <YEnY5hWLT/en7kw1@hirez.programming.kicks-ass.net>
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On Thu 11-03-21 09:46:30, Peter Zijlstra wrote:
> On Wed, Mar 10, 2021 at 06:13:21PM -0800, Mike Kravetz wrote:
> > from irq context.  Changing the check in the code from !in_task to
> > in_atomic would handle the situations when called with irqs disabled.
> 
> It does not. local_irq_disable() does not change preempt_count().

You are right. Earlier I was suggesting to check of irq_disabled() as
well http://lkml.kernel.org/r/YD4I+VPr3UNt063H@dhcp22.suse.cz

back then it was not really clear to me that in fact we do care about
spin locks more than irq disabled code. I am not even sure whether we
need to care about irq disabled regions without any locks held that
wouldn't be covered by in_atomic. But it would be safer to add
irq_disabled check as well.

-- 
Michal Hocko
SUSE Labs