cfq-iosched: fix a rcu warning

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@intel.com>
Cc: stable@kernel.org # after ab4bd22d
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index f3799432676d53cc3648c9ab6801fe4fd084b911..fd566c1e2617f8ff464defab7684ea865787655f 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -2773,11 +2773,14 @@ static void __cfq_exit_single_io_context(struct cfq_data *cfqd,
        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]);