io_uring: mem-account pbuf buckets

Potentially, someone may create as many pbuf bucket as there are indexes
in an xarray without any other restrictions bounding our memory usage,
put memory needed for the buckets under memory accounting.

Cc: <stable@vger.kernel.org>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/d34c452e45793e978d26e2606211ec9070d329ea.1659622312.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/kbuf.c

@@ -436,7 +436,7 @@ int io_provide_buffers(struct io_kiocb *req, unsigned int issue_flags)
 
 	bl = io_buffer_get_list(ctx, p->bgid);
 	if (unlikely(!bl)) {
-		bl = kzalloc(sizeof(*bl), GFP_KERNEL);
+		bl = kzalloc(sizeof(*bl), GFP_KERNEL_ACCOUNT);
 		if (!bl) {
 			ret = -ENOMEM;
 			goto err;