linux-kernel - [02/85] printk: Fix rq->lock vs logbuf

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Message-ID: <lsq.1374674565.515556061@decadent.org.uk>
Date:	Wed, 24 Jul 2013 15:02:45 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
	"Bu, Yitian" <ybu@....qualcomm.com>,
	"Thomas Gleixner" <tglx@...utronix.de>
Subject: [02/85] printk: Fix rq->lock vs logbuf_lock unlock lock inversion

3.2.49-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: "Bu, Yitian" <ybu@....qualcomm.com>

commit dbda92d16f8655044e082930e4e9d244b87fde77 upstream.

commit 07354eb1a74d1 ("locking printk: Annotate logbuf_lock as raw")
reintroduced a lock inversion problem which was fixed in commit
0b5e1c5255 ("printk: Release console_sem after logbuf_lock"). This
happened probably when fixing up patch rejects.

Restore the ordering and unlock logbuf_lock before releasing
console_sem.

Signed-off-by: ybu <ybu@....qualcomm.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Link: http://lkml.kernel.org/r/E807E903FE6CBE4D95E420FBFCC273B827413C@nasanexd01h.na.qualcomm.com
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/printk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -813,9 +813,9 @@ static int console_trylock_for_printk(un
 		}
 	}
 	printk_cpu = UINT_MAX;
+	raw_spin_unlock(&logbuf_lock);
 	if (wake)
 		up(&console_sem);
-	raw_spin_unlock(&logbuf_lock);
 	return retval;
 }
 static const char recursion_bug_msg [] =

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