Re: [PATCH 2/2] io_uring: don't block level reissue off completion path

[Fabian Ebner <f.ebner@proxmox.com>]

Am 27.07.21 um 18:58 schrieb Jens Axboe:
> Some setups, like SCSI, can throw spurious -EAGAIN off the softirq
> completion path. Normally we expect this to happen inline as part
> of submission, but apparently SCSI has a weird corner case where it
> can happen as part of normal completions.
> 
> This should be solved by having the -EAGAIN bubble back up the stack
> as part of submission, but previous attempts at this failed and we're
> not just quite there yet. Instead we currently use REQ_F_REISSUE to
> handle this case.
> 
> For now, catch it in io_rw_should_reissue() and prevent a reissue
> from a bogus path.
> 
> Cc: stable@vger.kernel.org
> Reported-by: Fabian Ebner <f.ebner@proxmox.com>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
>   fs/io_uring.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 6ba101cd4661..83f67d33bf67 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -2447,6 +2447,12 @@ static bool io_rw_should_reissue(struct io_kiocb *req)
>   	 */
>   	if (percpu_ref_is_dying(&ctx->refs))
>   		return false;
> +	/*
> +	 * Play it safe and assume not safe to re-import and reissue if we're
> +	 * not in the original thread group (or in task context).
> +	 */
> +	if (!same_thread_group(req->task, current) || !in_task())
> +		return false;
>   	return true;
>   }
>   #else
> 

Hi,

thank you for the fix! This does indeed prevent the panic (with 5.11.22) 
and hang (with 5.13.3) with my problematic workload.

Best Regards,
Fabian