io_uring: fix a memory leak of buffer group list on exit

If we use a buffer group ID that is large enough to require io_uring
to allocate it, then we don't correctly free it if the cleanup is
deferred to the ring exit. The explicit removal paths are fine.

Fixes: 9cfc7e9 ("io_uring: get rid of hashed provided buffer groups")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -11065,6 +11065,7 @@ static void io_destroy_buffers(struct io_ring_ctx *ctx)
 	xa_for_each(&ctx->io_bl_xa, index, bl) {
 		xa_erase(&ctx->io_bl_xa, bl->bgid);
 		__io_remove_buffers(ctx, bl, -1U);
+		kfree(bl);
 	}
 
 	while (!list_empty(&ctx->io_buffers_pages)) {