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/block/blk-ioc.c b/block/blk-ioc.c
index 012f065..d4ed600 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -35,9 +35,9 @@
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 @@
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 @@
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 @@
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;
}