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    Subject[PATCH] [78/99] cfq-iosched: fix a rcu warning
    Date
    2.6.35-longterm review patch.  If anyone has any objections, please let me know.

    ------------------
    From: Shaohua Li <shaohua.li@intel.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@intel.com>
    Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
    Signed-off-by: Andi Kleen <ak@linux.intel.com>

    ---
    block/cfq-iosched.c | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    Index: linux-2.6.35.y/block/cfq-iosched.c
    ===================================================================
    --- linux-2.6.35.y.orig/block/cfq-iosched.c
    +++ linux-2.6.35.y/block/cfq-iosched.c
    @@ -2615,11 +2615,14 @@ 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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