linux-kernel - Re: [PATCH] hugetlb: select PREEMPT_COUNT if HUGETLB_PAGE for in

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Date:   Thu, 11 Mar 2021 10:01:22 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>, tglx@...utronix.de,
        john.ogness@...utronix.de, urezki@...il.com, ast@...com,
        Eric Dumazet <edumazet@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] hugetlb: select PREEMPT_COUNT if HUGETLB_PAGE for
 in_atomic use

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