Commit d9c7d394 authored by Nikanth Karthikesan's avatar Nikanth Karthikesan Committed by Jens Axboe
Browse files

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: default avatarNikanth Karthikesan <knikanth@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent 1d589bb1

block/blk-ioc.c

+6 −6
Original line number Diff line number Diff line
@@ -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;

	}

block/cfq-iosched.c

+1 −1
Original line number Diff line number Diff line
@@ -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;

	}

}

include/linux/iocontext.h

+3 −3
Original line number Diff line number Diff line
@@ -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;

	}

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