Re: [Intel-wired-lan] [PATCH] [PATCH iwl-net] idpf: Acquire the lock before accessing the xn->salt

[Alexander Lobakin <aleksander.lobakin@intel.com>]

From: Manoj Vishwanathan <manojvishy@google.com>
Date: Mon,  5 Aug 2024 18:21:59 +0000

> The transaction salt was being accessed before acquiring the
> idpf_vc_xn_lock when idpf has to forward the virtchnl reply.

You need to explain in details here what issue you have faced due to
that, how to reproduce it and how this fix does help.
Otherwise, it's impossible to suggest what is happening and how to test
whether the fix is correct.

> 
> Fixes: 34c21fa894a1a (“idpf: implement virtchnl transaction manager”)
> Signed-off-by: Manoj Vishwanathan <manojvishy@google.com>
> ---
>  drivers/net/ethernet/intel/idpf/idpf_virtchnl.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/intel/idpf/idpf_virtchnl.c b/drivers/net/ethernet/intel/idpf/idpf_virtchnl.c
> index 70986e12da28..30eec674d594 100644
> --- a/drivers/net/ethernet/intel/idpf/idpf_virtchnl.c
> +++ b/drivers/net/ethernet/intel/idpf/idpf_virtchnl.c
> @@ -612,14 +612,15 @@ idpf_vc_xn_forward_reply(struct idpf_adapter *adapter,
>  		return -EINVAL;
>  	}
>  	xn = &adapter->vcxn_mngr->ring[xn_idx];
> +	idpf_vc_xn_lock(xn);
>  	salt = FIELD_GET(IDPF_VC_XN_SALT_M, msg_info);

The lock can be taken here after the FIELD_GET(), not before, to reduce
the critical/locked section execution time.

>  	if (xn->salt != salt) {
>  		dev_err_ratelimited(&adapter->pdev->dev, "Transaction salt does not match (%02x != %02x)\n",
>  				    xn->salt, salt);
> +		idpf_vc_xn_unlock(xn);
>  		return -EINVAL;
>  	}
>  
> -	idpf_vc_xn_lock(xn);
>  	switch (xn->state) {
>  	case IDPF_VC_XN_WAITING:
>  		/* success */

Thanks,
Olek