linux-kernel - Re: suspend regression in 4.1-rc1

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Date:	Mon, 18 May 2015 10:49:24 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: suspend regression in 4.1-rc1

On (05/17/15 20:50), Michal Hocko wrote:
> 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:
> 

Hello,

JFI, I see quite similar behaviour on my laptop (linux-next doesn't boot:
blank screen and fans on). I've tried to bisect yesterday, but it didn't
go well, showing that the first bad commit is '31ccd0e66d41' (nonsense);
it seems that the root cause is somewhere between next-20150505 (ok) and
next-20150506 (boot failure). I'll continue bisecting.

	-ss

> 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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