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>
diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h
index 08b987b..dd05434 100644
--- a/include/linux/iocontext.h
+++ b/include/linux/iocontext.h
@@ -64,7 +64,7 @@
* 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 @@
* 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;
}