linux-kernel - [PATCH 3.19.y-ckt 123/210] kernel/panic.c: turn off locks debug before releasing console lock

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Message-Id: <1454030348-17736-124-git-send-email-kamal@canonical.com>
Date:	Thu, 28 Jan 2016 17:17:41 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Vitaly Kuznetsov <vkuznets@...hat.com>,
	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>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 123/210] kernel/panic.c: turn off locks debug before releasing console lock

3.19.8-ckt14 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Vitaly Kuznetsov <vkuznets@...hat.com>

commit 7625b3a0007decf2b135cb47ca67abc78a7b1bc1 upstream.

Commit 08d78658f393 ("panic: release stale console lock to always get the
logbuf printed out") introduced an 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>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 kernel/panic.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/panic.c b/kernel/panic.c
index 1871216..ea4e4ba 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -151,8 +151,11 @@ 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();
 
-- 
1.9.1