Re: [PATCH 1/4] fuse: {io-uring} Use READ_ONCE in fuse_uring_send_in_task

[Joanne Koong <joannelkoong@xxxxxxxxx>]

On Fri, Jan 24, 2025 at 8:47 AM Bernd Schubert <bschubert@xxxxxxx> wrote:
>
> The value is read from another task without, while the task that
> had set the value was holding queue->lock. Better use READ_ONCE
> to ensure the compiler cannot optimize the read.
>
> Fixes: 284985711dc5 ("fuse: Allow to queue fg requests through io-uring")
> Signed-off-by: Bernd Schubert <bschubert@xxxxxxx>
> ---
>  fs/fuse/dev_uring.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
> index 5c9b5a5fb7f7539149840378e224eb640cf8ef08..1834c1933d2bbab0342257fde4b030f06506c55d 100644
> --- a/fs/fuse/dev_uring.c
> +++ b/fs/fuse/dev_uring.c
> @@ -1202,10 +1202,12 @@ static void fuse_uring_send_in_task(struct io_uring_cmd *cmd,
>  {
>         struct fuse_ring_ent *ent = uring_cmd_to_ring_ent(cmd);
>         struct fuse_ring_queue *queue = ent->queue;
> +       struct fuse_req *req;
>         int err;
>
>         if (!(issue_flags & IO_URING_F_TASK_DEAD)) {
> -               err = fuse_uring_prepare_send(ent);
> +               req = READ_ONCE(ent->fuse_req);
> +               err = fuse_uring_prepare_send(ent, req);

Hi Bernd,  did you mean something like this?:

diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
index 5c9b5a5fb7f7..692e97f9870d 100644
--- a/fs/fuse/dev_uring.c
+++ b/fs/fuse/dev_uring.c
@@ -676,7 +676,7 @@ static int fuse_uring_copy_to_ring(struct
fuse_ring_ent *ent,

 static int fuse_uring_prepare_send(struct fuse_ring_ent *ent)
 {
-       struct fuse_req *req = ent->fuse_req;
+       struct fuse_req *req = READ_ONCE(ent->fuse_req);
        int err;

        err = fuse_uring_copy_to_ring(ent, req);

I'm on top of the for-next tree but I'm not seeing where
fuse_uring_prepare_send() takes in req as an arg.


Thanks,
Joanne

>                 if (err) {
>                         fuse_uring_next_fuse_req(ent, queue, issue_flags);
>                         return;
>
> --
> 2.43.0
>