linux-kernel - [PATCH] panic: turn off locks debug before releasing console lock

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Date:	Mon, 16 Nov 2015 19:20:14 +0100
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Jiri Kosina <jkosina@...e.cz>, Baoquan He <bhe@...hat.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Xie XiuQi <xiexiuqi@...wei.com>,
	Seth Jennings <sjenning@...hat.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>, Jan Kara <jack@...e.cz>,
	Petr Mladek <pmladek@...e.cz>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Subject: [PATCH] panic: turn off locks debug before releasing console lock

Commit 08d78658f393 ("panic: release stale console lock to always get the
logbuf printed out") introduced unwanted bad unlock balance report when
panic() is called directly and not from OOPS (e.g. from out_of_memory()).
The difference is that in case of OOPS we disable locks debug in
oops_enter() and on direct panic call nobody does that.

Fixes: 08d78658f393 ("panic: release stale console lock to always get the logbuf printed out")
Reported-by: kernel test robot <ying.huang@...ux.intel.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc: Jiri Kosina <jkosina@...e.cz>
Cc: Baoquan He <bhe@...hat.com>
Cc: Prarit Bhargava <prarit@...hat.com>
Cc: Xie XiuQi <xiexiuqi@...wei.com>
Cc: Seth Jennings <sjenning@...hat.com>
Cc: "K. Y. Srinivasan" <kys@...rosoft.com>
Cc: Jan Kara <jack@...e.cz>
Cc: Petr Mladek <pmladek@...e.cz>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
---
The original plan was to replace this patch with less hackish implementation
from Jan's "printk: Softlockup avoidance" series but it seems it didn't get
merged in 4.4 so we still need some band-aid for now.
---
 kernel/panic.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/panic.c b/kernel/panic.c
index 4579dbb..4b150bc 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -152,8 +152,11 @@ void panic(const char *fmt, ...)
 	 * We may have ended up stopping the CPU holding the lock (in
 	 * smp_send_stop()) while still having some valuable data in the console
 	 * buffer.  Try to acquire the lock then release it regardless of the
-	 * result.  The release will also print the buffers out.
+	 * result.  The release will also print the buffers out.  Locks debug
+	 * should be disabled to avoid reporting bad unlock balance when
+	 * panic() is not being callled from OOPS.
 	 */
+	debug_locks_off();
 	console_trylock();
 	console_unlock();
 
-- 
2.4.3

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