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Commit f9e1aedc authored by NeilBrown's avatar NeilBrown Committed by J. Bruce Fields
Browse files

sunrpc/cache: remove races with queuing an upcall. 



We currently queue an upcall after setting CACHE_PENDING,
and dequeue after clearing CACHE_PENDING.
So a request should only be present when CACHE_PENDING is set.

However we don't combine the test and the enqueue/dequeue in
a protected region, so it is possible (if unlikely) for a race
to result in a request being queued without CACHE_PENDING set,
or a request to be absent despite CACHE_PENDING.

So: include a test for CACHE_PENDING inside the regions of
enqueue and dequeue where queue_lock is held, and abort
the operation if the value is not as expected.

Also remove the early 'return' from cache_dequeue() to ensure that it
always removes all entries: As there is no locking between setting
CACHE_PENDING and calling sunrpc_cache_pipe_upcall it is not
inconceivable for some other thread to clear CACHE_PENDING and then
someone else to set it and call sunrpc_cache_pipe_upcall, both before
the original threads completed the call.

With this, it perfectly safe and correct to:
 - call cache_dequeue() if and only if we have just
   cleared CACHE_PENDING
 - call sunrpc_cache_pipe_upcall() (via cache_make_upcall)
   if and only if we have just set CACHE_PENDING.

Reported-by: default avatarBodo Stroesser <bstroesser@ts.fujitsu.com>
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
Signed-off-by: default avatarBodo Stroesser <bstroesser@ts.fujitsu.com>
Signed-off-by: default avatarJ. Bruce Fields <bfields@redhat.com>
parent d08d32e6

net/sunrpc/cache.c

+29 −11
Original line number Diff line number Diff line
@@ -1036,23 +1036,32 @@ static int cache_release(struct inode *inode, struct file *filp, 


static void cache_dequeue(struct cache_detail *detail, struct cache_head *ch)

{

	struct cache_queue *cq;

	struct cache_queue *cq, *tmp;

	struct cache_request *cr;

	struct list_head dequeued;



	INIT_LIST_HEAD(&dequeued);

	spin_lock(&queue_lock);

	list_for_each_entry(cq, &detail->queue, list)

	list_for_each_entry_safe(cq, tmp, &detail->queue, list)

		if (!cq->reader) {

			struct cache_request *cr = container_of(cq, struct cache_request, q);

			cr = container_of(cq, struct cache_request, q);

			if (cr->item != ch)

				continue;

			if (test_bit(CACHE_PENDING, &ch->flags))

				/* Lost a race and it is pending again */

				break;

			if (cr->readers != 0)

				continue;

			list_del(&cr->q.list);

			list_move(&cr->q.list, &dequeued);

		}

	spin_unlock(&queue_lock);

	while (!list_empty(&dequeued)) {

		cr = list_entry(dequeued.next, struct cache_request, q.list);

		list_del(&cr->q.list);

		cache_put(cr->item, detail);

		kfree(cr->buf);

		kfree(cr);

			return;

	}

	spin_unlock(&queue_lock);

}



/*
@@ -1166,6 +1175,7 @@ int sunrpc_cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h) 


	char *buf;

	struct cache_request *crq;

	int ret = 0;



	if (!detail->cache_request)

		return -EINVAL;
@@ -1191,10 +1201,18 @@ int sunrpc_cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h) 
	crq->len = 0;

	crq->readers = 0;

	spin_lock(&queue_lock);

	if (test_bit(CACHE_PENDING, &h->flags))

		list_add_tail(&crq->q.list, &detail->queue);

	else

		/* Lost a race, no longer PENDING, so don't enqueue */

		ret = -EAGAIN;

	spin_unlock(&queue_lock);

	wake_up(&queue_wait);

	return 0;

	if (ret == -EAGAIN) {

		kfree(buf);

		kfree(crq);

	}

	return ret;

}

EXPORT_SYMBOL_GPL(sunrpc_cache_pipe_upcall);