linux-kernel - Re: [PATCH v4] x86/mce: Avoid infinite loop for copy from user recovery

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Message-ID: <20210120121812.GF825@zn.tnic>
Date:   Wed, 20 Jan 2021 13:18:12 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     x86@...nel.org, Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v4] x86/mce: Avoid infinite loop for copy from user
 recovery

On Tue, Jan 19, 2021 at 03:57:59PM -0800, Luck, Tony wrote:
> But the real validation folks took my patch and found that it has
> destabilized cases 1 & 2 (and case 3 also chokes if you repeat a few
> more times). System either hangs or panics. Generally before 100
> injection/conumption cycles.

Hmm, that mce_count increment and check stuff might turn out to be
fragile in the face of a race condition. But I don't see it...

> So if you see anything obviously broken, let me know. Otherwise I'll
> be poking around at the patch to figure out what is wrong.

Yah, some printk sprinkling might be a good start. But debugging in that
atomic context is always nasty. ;-\

-- 
Regards/Gruss,
    Boris.

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