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

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Date:	Tue, 19 May 2015 09:12:59 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	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" <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: suspend regression in 4.1-rc1

On Mon 18-05-15 10:10:50, Linus Torvalds wrote:
> On Mon, May 18, 2015 at 2:31 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > Subject: watchdog: Fix merge 'conflict'
> >
> > Two watchdog changes that came through different trees had a non
> > conflicting conflict, that is, one changed the semantics of a variable
> > but no actual code conflict happened. So the merge appeared fine, but
> > the resulting code did not behave as expected.
> 
> Ok, I see that people are still discussing this, but I'll apply it
> as-is since I want to get rc4 out the door, and I guess people can
> tweak this if there's anything else we want to do longer-term.

The final patch from Peter has a typo. Without the following the system
deadlocks obviously:
---
>From 215266efd5e14938d14f0f4258a70fb32f6a455b Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@...e.cz>
Date: Tue, 19 May 2015 09:07:27 +0200
Subject: [PATCH] watchdog: fix double lock in watchdog_nmi_enable_all

ab992dc38f9a ("watchdog: Fix merge 'conflict'") has introduced an
obvious deadlock because of a typo. watchdog_proc_mutex should be
unlocked on exit.

Thanks to Miroslav Benes who was staring at the code with me and noticed
this.

Signed-off-by: Michal Hocko <mhocko@...e.cz>
---
 kernel/watchdog.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 506edcc500c4..581a68a04c64 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -621,7 +621,7 @@ void watchdog_nmi_enable_all(void)
 	put_online_cpus();
 
 unlock:
-	mutex_lock(&watchdog_proc_mutex);
+	mutex_unlock(&watchdog_proc_mutex);
 }
 
 void watchdog_nmi_disable_all(void)
-- 
2.1.4

-- 
Michal Hocko
SUSE Labs
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