linux-kernel - suspend regression in 4.1-rc1

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Date:	Sun, 17 May 2015 20:50:41 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ulrich Obergfell <uobergfe@...hat.com>,
	Don Zickus <dzickus@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Kevin Hilman <khilman@...nel.org>,
	Ulf Hansson <ulf.hansson@...aro.org>, linux-pm@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: suspend regression in 4.1-rc1

Hi,
s2ram broke after 4.1-rc1 for me. The second s2ram simply doesn't wake
up (fans turn on but the screen is off). I have even noticed fans
starting also while suspended in some instances (which was especially
annoying when it happened on the way home from work).
I've tried /sys/power/pm_test and the issue starts at processors mode.
Nothing really interesting shows up in the netconsole but I didn't get
to a more detailed testing there.

I've tried to bisect this as 4.0 works reliably. This was tricky though
because the first bad commit is a merge:

commit 1dcf58d6e6e6eb7ec10e9abc56887b040205b06f
Merge: 80dcc31fbe55 e4b0db72be24
Author: Linus Torvalds <torvalds@...ux-foundation.org>
Date:   Tue Apr 14 16:49:17 2015 -0700

    Merge branch 'akpm' (patches from Andrew)

The merge commit is empty and both 80dcc31fbe55 and e4b0db72be24 work
properly but the merge is bad. So it seems like some of the commits in
either branch has a side effect which needs other branch in order to
reproduce.

So've tried to bisect ^80dcc31fbe55 e4b0db72be24 and merged 80dcc31fbe55
in each step. This lead to:

commit 195daf665a6299de98a4da3843fed2dd9de19d3a
Author: Ulrich Obergfell <uobergfe@...hat.com>
Date:   Tue Apr 14 15:44:13 2015 -0700

    watchdog: enable the new user interface of the watchdog mechanism

The patch doesn't revert because of follow up changes so I have reverted
all three:
692297d8f968 ("watchdog: introduce the hardlockup_detector_disable() function")
b2f57c3a0df9 ("watchdog: clean up some function names and arguments")
195daf665a62 ("watchdog: enable the new user interface of the watchdog mechanism")

on top of my current Linus tree (4cfceaf0c087f47033f5e61a801f4136d6fb68c6)
and the issue is gone. I have hard time to understand what these 3 could have
to do with suspend path, though.

Then I've tried to bisect the other branch and merge 195daf665a62 during
each step to find out which patch starts failing. This lead to an even
weirder commit a1e12da4796a ("perf tools: Add 'I' event modifier for
exclude_idle bit") but maybe I've just screwed something on the way.

I will continue debugging tomorrow but any hints would be helpful.
-- 
Michal Hocko
SUSE Labs
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