Re: [PATCH] io_uring/uring_cmd: use cached cmd_op in io_uring_cmd_sock()

[Jann Horn <jannh@google.com>]

On Thu, Jan 23, 2025 at 1:32 AM Jens Axboe <axboe@kernel.dk> wrote:
> io_uring_cmd_sock() does a read of cmd->sqe->cmd_op, which may look
> like it's the userspace shared SQE, but it's a copy at this point.
> Use cmd->cmd_op rather than dip into the allocated SQE copy - it's
> both simpler and faster and leaves less room for confusion.
>
> Link: https://lore.kernel.org/r/20250121-uring-sockcmd-fix-v1-1-add742802a29@google.com
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>
> ---
>
> diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
> index fc94c465a985..3993c9339ac7 100644
> --- a/io_uring/uring_cmd.c
> +++ b/io_uring/uring_cmd.c
> @@ -350,7 +350,7 @@ int io_uring_cmd_sock(struct io_uring_cmd *cmd, unsigned int issue_flags)
>         if (!prot || !prot->ioctl)
>                 return -EOPNOTSUPP;
>
> -       switch (cmd->sqe->cmd_op) {
> +       switch (cmd->cmd_op) {

Ah, yeah, this does look better than the READ_ONCE() I suggested.