linux-kernel - [075/107] cfq-iosched: fix a rcu warning

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Message-Id: <20110708001700.044146952@clark.kroah.org>
Date:	Thu, 07 Jul 2011 17:16:47 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Shaohua Li <shaohua.li@...el.com>,
	Jens Axboe <jaxboe@...ionio.com>
Subject: [075/107] cfq-iosched: fix a rcu warning

2.6.39-stable review patch.  If anyone has any objections, please let us know.

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

From: Shaohua Li <shaohua.li@...el.com>

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 file changed, 4 insertions(+), 1 deletion(-)

--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2704,11 +2704,14 @@ static void __cfq_exit_single_io_context
 	smp_wmb();
 	cic->key = cfqd_dead_key(cfqd);
 
+	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[BLK_RW_ASYNC]) {
 		cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_ASYNC]);


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