linux-kernel - [PATCH 29/91] cfq-iosched: fix a rcu warning

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Message-Id: <20120205220950.684814014@pcw.home.local>
Date:	Sun, 05 Feb 2012 23:10:18 +0100
From:	Willy Tarreau <w@....eu>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Shaohua Li <shaohua.li@...el.com>,
	Jens Axboe <jaxboe@...ionio.com>,
	Greg KH <gregkh@...uxfoundation.org>
Subject: [PATCH 29/91] cfq-iosched: fix a rcu warning

2.6.27-longterm review patch.  If anyone has any objections, please let us know.

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

commit 3181faa85bda3dc3f5e630a1846526c9caaa38e3 upstream.

I got a rcu warnning at boot. the ioc->ioc_data is rcu_deferenced, but
doesn't hold rcu_read_lock.

Signed-off-by: Shaohua Li <shaohua.li@...el.com>
Signed-off-by: Jens Axboe <jaxboe@...ionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
---
 block/cfq-iosched.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

Index: longterm-2.6.27/block/cfq-iosched.c
===================================================================
--- longterm-2.6.27.orig/block/cfq-iosched.c	2012-02-05 22:34:38.850917663 +0100
+++ longterm-2.6.27/block/cfq-iosched.c	2012-02-05 22:34:38.987917155 +0100
@@ -1286,11 +1286,14 @@
 	cic->dead_key = (unsigned long) cic->key;
 	cic->key = NULL;
 
+	rcu_read_lock();
 	if (rcu_dereference(ioc->ioc_data) == cic) {
+		rcu_read_unlock();
 		spin_lock(&ioc->lock);
 		rcu_assign_pointer(ioc->ioc_data, NULL);
 		spin_unlock(&ioc->lock);
-	}
+	} else
+		rcu_read_unlock();
 
 	if (cic->cfqq[ASYNC]) {
 		cfq_exit_cfqq(cfqd, cic->cfqq[ASYNC]);


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