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

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Date:   Wed, 20 Jan 2021 17:17:25 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     "x86@...nel.org" <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-kernel@...r.kernel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: RE: [PATCH v4] x86/mce: Avoid infinite loop for copy from user
 recovery

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

Some very light printk sprinkling (one message in queue_task_work() in atomic
context, one each in kill_me_now() and kill_me_maybe() to check when task_work
actually called them.

Cases 1 & 2 (user & normal copyin) now work just fine (hundreds of iterations).

Case 3 (my futex test) just hangs with only two characters making it to the serial port "[ "

Deeply strange.

-Tony