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Date: Tue, 15 Apr 2014 15:54:53 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Luis Henriques <luis.henriques@canonical.com>
Cc: Eric Piel <eric.piel@tremplin-utc.net>,
        Robert Moore <robert.moore@intel.com>, Lv Zheng <lv.zheng@intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Len Brown <lenb@kernel.org>, linux-acpi@vger.kernel.org,
        linux-kernel@vger.kernel.org, Christoph Lameter <cl@linux.com>
Subject: Re: BUG: using __this_cpu_write() in preemptible [00000000] code:
 systemd-udevd/497
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On Tue, 15 Apr 2014 00:55:50 +0100 Luis Henriques <luis.henriques@canonical.com> wrote:

> (Cc'ing both lis3lv02d and ACPI maintainers)
> 
> Since commit 188a81409ff7de1c5aae947a96356ddd8ff4aaa3 ("percpu: add
> preemption checks to __this_cpu ops") I've been seeing the following:
> 
> [   10.485588] hp_accel: hardware type HPB64xx found
> [   10.485772] BUG: using __this_cpu_write() in preemptible [00000000] code: systemd-udevd/497
> [   10.485777] caller is __this_cpu_preempt_check+0x13/0x20
> [   10.485781] CPU: 3 PID: 497 Comm: systemd-udevd Tainted: G        W     3.15.0-rc1 #9
> [   10.485783] Hardware name: Hewlett-Packard HP EliteBook 8470p/179B, BIOS 68ICF Ver. F.02 04/27/2012
> [   10.485785]  ffffffff81a14db5 ffff88022c80b8e0 ffffffff81604ba4 0000000000000003
> [   10.485789]  ffff88022c80b908 ffffffff81313431 0000000000000000 0000000000000032
> [   10.485793]  00000000000003e8 ffff88022c80b918 ffffffff81313473 ffff88022c80b928
> [   10.485796] Call Trace:
> [   10.485802]  [<ffffffff81604ba4>] dump_stack+0x4e/0x7a
> [   10.485805]  [<ffffffff81313431>] check_preemption_disabled+0xe1/0xf0
> [   10.485808]  [<ffffffff81313473>] __this_cpu_preempt_check+0x13/0x20
> [   10.485813]  [<ffffffff810e4eb8>] touch_nmi_watchdog+0x28/0x40

Presumably touch_softlockup_watchdog() being called with preemption
enabled.  Which is a legitimate thing to do and there's no point in
disabling preemption just to squish a runtime warning.

Christoph, this thing has iirc caught a couple of very minor bugs but
it is being quite a pain in the rear.   I'm inclined to revert?
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