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, 6 insertions, 6 deletions

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 012f065ac8e2..d4ed6000147d 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -35,9 +35,9 @@ int put_io_context(struct io_context *ioc)
         if (ioc == NULL)
                 return 1;
 
-        BUG_ON(atomic_read(&ioc->refcount) == 0);
+        BUG_ON(atomic_long_read(&ioc->refcount) == 0);
 
-        if (atomic_dec_and_test(&ioc->refcount)) {
+        if (atomic_long_dec_and_test(&ioc->refcount)) {
                 rcu_read_lock();
                 if (ioc->aic && ioc->aic->dtor)
                         ioc->aic->dtor(ioc->aic);
@@ -90,7 +90,7 @@ struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
 
         ret = kmem_cache_alloc_node(iocontext_cachep, gfp_flags, node);
         if (ret) {
-                atomic_set(&ret->refcount, 1);
+                atomic_long_set(&ret->refcount, 1);
                 atomic_set(&ret->nr_tasks, 1);
                 spin_lock_init(&ret->lock);
                 ret->ioprio_changed = 0;
@@ -151,7 +151,7 @@ struct io_context *get_io_context(gfp_t gfp_flags, int node)
                 ret = current_io_context(gfp_flags, node);
                 if (unlikely(!ret))
                         break;
-        } while (!atomic_inc_not_zero(&ret->refcount));
+        } while (!atomic_long_inc_not_zero(&ret->refcount));
 
         return ret;
 }
@@ -163,8 +163,8 @@ void copy_io_context(struct io_context **pdst, struct io_context **psrc)
         struct io_context *dst = *pdst;
 
         if (src) {
-                BUG_ON(atomic_read(&src->refcount) == 0);
-                atomic_inc(&src->refcount);
+                BUG_ON(atomic_long_read(&src->refcount) == 0);
+                atomic_long_inc(&src->refcount);
                 put_io_context(dst);
                 *pdst = src;
         }