linux-kernel - Re: [PATCH] watchdog: hpwdt: Remove spinlock acquire and BIOS calls from NMI context

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Date:   Thu, 15 Feb 2018 20:48:28 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jerry Hoemann <jerry.hoemann@....com>
Cc:     Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Dave Hansen <dave@...1.net>, hpa@...or.com, tglx@...utronix.de,
        torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
        dwmw@...zon.co.uk, linux-tip-commits@...r.kernel.org,
        Arjan van de Ven <arjan@...radead.org>,
        linux-watchdog@...r.kernel.org
Subject: Re: [PATCH] watchdog: hpwdt: Remove spinlock acquire and BIOS calls
 from NMI context

On Thu, Feb 15, 2018 at 10:44:44AM -0700, Jerry Hoemann wrote:
> Is your desire to remove of the firmware callback/spinlock in hpwdt_pretimeout
> related to David Woodhouse patch set:

That's the work that made us find this code, but no, even without that,
code like that is entirely dodgy. NMI code needs to be very careful and
firmware just isn't something I trust to get things right. Worse, its
not something we can fix.

And using spnilock from NMI context is just wrong, if anything it needs
be raw_spnilock but even then, yuck.