nvmet-tcp: fix a memory leak when releasing a queue

page_frag_free() won't completely release the memory
allocated for the commands, the cache page must be explicitly
freed by calling __page_frag_cache_drain().

This bug can be easily reproduced by repeatedly
executing the following command on the initiator:

$echo 1 > /sys/devices/virtual/nvme-fabrics/ctl/nvme0/reset_controller

Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: John Meneghini <jmeneghi@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/tcp.c

@@ -1428,6 +1428,7 @@ static void nvmet_tcp_uninit_data_in_cmds(struct nvmet_tcp_queue *queue)
 
 static void nvmet_tcp_release_queue_work(struct work_struct *w)
 {
+	struct page *page;
 	struct nvmet_tcp_queue *queue =
 		container_of(w, struct nvmet_tcp_queue, release_work);
 
@@ -1447,6 +1448,8 @@ static void nvmet_tcp_release_queue_work(struct work_struct *w)
 		nvmet_tcp_free_crypto(queue);
 	ida_simple_remove(&nvmet_tcp_queue_ida, queue->idx);
 
+	page = virt_to_head_page(queue->pf_cache.va);
+	__page_frag_cache_drain(page, queue->pf_cache.pagecnt_bias);
 	kfree(queue);
 }