linux-kernel - Re: Question about qspinlock nest

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Message-ID: <20190111173648.GH4729@zn.tnic>
Date:   Fri, 11 Jan 2019 18:36:48 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Zhenzhong Duan <zhenzhong.duan@...cle.com>,
        Waiman Long <longman@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        SRINIVAS <srinivas.eeda@...cle.com>
Subject: Re: Question about qspinlock nest

On Fri, Jan 11, 2019 at 10:16:38AM +0100, Peter Zijlstra wrote:
> > Not for debug exception, for MCE exception handler I found below two:
> > 
> > do_machine_check->mce_report_event->schedule_work

That has been the case at least since 2009. We probably never hit it or
I've never seen a deadlock caused by it.

> > do_machine_check->force_sig->force_sig_info

This does:

        ist_begin_non_atomic(regs);
        local_irq_enable();

before forcing the signal. And there's blurb above
ist_begin_non_atomic() why it is OK to schedule when the exception came
from usermode.

-- 
Regards/Gruss,
    Boris.

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