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, 3 insertions, 3 deletions

diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index 08b987bccf89..dd05434fa45f 100644
--- a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -64,7 +64,7 @@ struct cfq_io_context {
  * and kmalloc'ed. These could be shared between processes.
  */
 struct io_context {
-        atomic_t refcount;
+        atomic_long_t refcount;
         atomic_t nr_tasks;
 
         /* all the fields below are protected by this lock */
@@ -91,8 +91,8 @@ static inline struct io_context *ioc_task_link(struct io_context *ioc)
          * if ref count is zero, don't allow sharing (ioc is going away, it's
          * a race).
          */
-        if (ioc && atomic_inc_not_zero(&ioc->refcount)) {
-                atomic_inc(&ioc->nr_tasks);
+        if (ioc && atomic_long_inc_not_zero(&ioc->refcount)) {
+                atomic_long_inc(&ioc->refcount);
                 return ioc;
         }