io_uring: correct size of overflow CQE calculation

If a 32b CQE is required, don't double the size of the overflow struct,
just add the size of the io_uring_cqe addition that is needed. This
avoids allocating too much memory, as the io_overflow_cqe size includes
the list member required to queue them too.

Fixes: e26dca6 ("io_uring: add support for IORING_SETUP_CQE_MIXED")
Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: axboe

io_uring/io_uring.c

@@ -756,7 +756,7 @@ static struct io_overflow_cqe *io_alloc_ocqe(struct io_ring_ctx *ctx,
 
 	if (cqe->flags & IORING_CQE_F_32 || ctx->flags & IORING_SETUP_CQE32) {
 		is_cqe32 = true;
-		ocq_size <<= 1;
+		ocq_size += sizeof(struct io_uring_cqe);
 	}
 
 	ocqe = kzalloc(ocq_size, gfp | __GFP_ACCOUNT);