Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 11 Jan 2019 18:36:48 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Zhenzhong Duan <zhenzhong.duan@oracle.com>,
        Waiman Long <longman@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        SRINIVAS <srinivas.eeda@oracle.com>
Subject: Re: Question about qspinlock nest
Message-ID: <20190111173648.GH4729@zn.tnic>
References: <e784a592-5dec-b0b3-6c70-d9ef775621d5@oracle.com>
 <910e9fb6-d0df-4711-fe2b-244b3c20eb82@redhat.com>
 <2eca6f60-3e8b-a389-27cb-8adbd9676607@oracle.com>
 <20190111091638.GK30894@hirez.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20190111091638.GK30894@hirez.programming.kicks-ass.net>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.

Good mailing practices for 400: avoid top-posting and trim the reply.