nvmet-tcp: fix page fragment cache leak in error path

nvmet-tcp: fix page fragment cache leak in error path

In nvmet_tcp_alloc_queue(), when a connection is closed during the
allocation process (e.g., nvmet_tcp_set_queue_sock() returns -ENOTCONN),
the error handling jumps to out_destroy_sq and then to out_ida_remove
without draining the page fragment cache.

Although nvmet_tcp_free_cmd() is called in some error paths to release
individual page fragments, the underlying page cache reference held by
queue->pf_cache is never released. The first allocation using pf_cache
is the call to nvmet_tcp_alloc_cmd() for queue->connect, which happens
after ida_alloc() returns successfully. This results in a page leak each
time a connection fails during allocation, which could lead to memory
exhaustion over time if connections are repeatedly opened and closed.

Fix this by calling page_frag_cache_drain() before freeing the queue
structure in the out_ida_remove label.

Fixes: 872d26a391da ("nvmet-tcp: add NVMe over TCP target driver")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Signed-off-by: Keith Busch <kbusch@kernel.org>