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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: Bodo Stroesser <bstroesser@ts.fujitsu.com> Signed-off-by: NeilBrown <neilb@suse.de> Signed-off-by: Bodo Stroesser <bstroesser@ts.fujitsu.com> Signed-off-by: J. Bruce Fields <bfields@redhat.com>
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d08d32e6e5
commit
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@ -1036,23 +1036,32 @@ static int cache_release(struct inode *inode, struct file *filp,
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static void cache_dequeue(struct cache_detail *detail, struct cache_head *ch)
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{
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struct cache_queue *cq;
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struct cache_queue *cq, *tmp;
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struct cache_request *cr;
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struct list_head dequeued;
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INIT_LIST_HEAD(&dequeued);
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spin_lock(&queue_lock);
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list_for_each_entry(cq, &detail->queue, list)
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list_for_each_entry_safe(cq, tmp, &detail->queue, list)
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if (!cq->reader) {
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struct cache_request *cr = container_of(cq, struct cache_request, q);
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cr = container_of(cq, struct cache_request, q);
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if (cr->item != ch)
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continue;
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if (test_bit(CACHE_PENDING, &ch->flags))
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/* Lost a race and it is pending again */
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break;
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if (cr->readers != 0)
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continue;
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list_del(&cr->q.list);
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spin_unlock(&queue_lock);
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cache_put(cr->item, detail);
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kfree(cr->buf);
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kfree(cr);
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return;
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list_move(&cr->q.list, &dequeued);
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}
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spin_unlock(&queue_lock);
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while (!list_empty(&dequeued)) {
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cr = list_entry(dequeued.next, struct cache_request, q.list);
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list_del(&cr->q.list);
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cache_put(cr->item, detail);
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kfree(cr->buf);
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kfree(cr);
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}
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}
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/*
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@ -1166,6 +1175,7 @@ int sunrpc_cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h)
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char *buf;
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struct cache_request *crq;
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int ret = 0;
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if (!detail->cache_request)
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return -EINVAL;
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@ -1191,10 +1201,18 @@ int sunrpc_cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h)
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crq->len = 0;
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crq->readers = 0;
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spin_lock(&queue_lock);
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list_add_tail(&crq->q.list, &detail->queue);
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if (test_bit(CACHE_PENDING, &h->flags))
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list_add_tail(&crq->q.list, &detail->queue);
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else
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/* Lost a race, no longer PENDING, so don't enqueue */
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ret = -EAGAIN;
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spin_unlock(&queue_lock);
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wake_up(&queue_wait);
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return 0;
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if (ret == -EAGAIN) {
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kfree(buf);
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kfree(crq);
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}
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return ret;
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}
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EXPORT_SYMBOL_GPL(sunrpc_cache_pipe_upcall);
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