io_uring: add buffer unmap helper

Add a helper for unmapping registered buffers, better than double
indexing and will be reused in the future.
Suggested-by: Bijan Mottahedeh <bijan.mottahedeh@oracle.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/66cbc6ea863be865bac7b7080ed6a3d5c542b71f.1618101759.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -8093,25 +8093,27 @@ static unsigned long rings_size(unsigned sq_entries, unsigned cq_entries,
 	return off;
 }
 
+static void io_buffer_unmap(struct io_ring_ctx *ctx, struct io_mapped_ubuf *imu)
+{
+	unsigned int i;
+
+	for (i = 0; i < imu->nr_bvecs; i++)
+		unpin_user_page(imu->bvec[i].bv_page);
+	if (imu->acct_pages)
+		io_unaccount_mem(ctx, imu->acct_pages);
+	kvfree(imu->bvec);
+	imu->nr_bvecs = 0;
+}
+
 static int io_sqe_buffers_unregister(struct io_ring_ctx *ctx)
 {
-	int i, j;
+	unsigned int i;
 
 	if (!ctx->user_bufs)
 		return -ENXIO;
 
-	for (i = 0; i < ctx->nr_user_bufs; i++) {
-		struct io_mapped_ubuf *imu = &ctx->user_bufs[i];
-
-		for (j = 0; j < imu->nr_bvecs; j++)
-			unpin_user_page(imu->bvec[j].bv_page);
-
-		if (imu->acct_pages)
-			io_unaccount_mem(ctx, imu->acct_pages);
-		kvfree(imu->bvec);
-		imu->nr_bvecs = 0;
-	}
-
+	for (i = 0; i < ctx->nr_user_bufs; i++)
+		io_buffer_unmap(ctx, &ctx->user_bufs[i]);
 	kfree(ctx->user_bufs);
 	ctx->user_bufs = NULL;
 	ctx->nr_user_bufs = 0;