block: prevent possible io_context->refcount overflow

Currently io_context has an atomic_t(32-bit) as refcount.  In the case of
cfq, for each device against whcih a task does I/O, a reference to the
io_context would be taken.  And when there are multiple process sharing
io_contexts(CLONE_IO) would also have a reference to the same io_context.

Theoretically the possible maximum number of processes sharing the same
io_context + the number of disks/cfq_data referring to the same io_context
can overflow the 32-bit counter on a very high-end machine.

Even though it is an improbable case, let us make it atomic_long_t.

Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 99ac4304d71..ef2f72d4243 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1282,7 +1282,7 @@ static void cfq_dispatch_request(struct cfq_data *cfqd, struct cfq_queue *cfqq)
         if (!cfqd->active_cic) {
                 struct cfq_io_context *cic = RQ_CIC(rq);
 
-                atomic_inc(&cic->ioc->refcount);
+                atomic_long_inc(&cic->ioc->refcount);
                 cfqd->active_cic = cic;
         }
 }