netdev - Re: [PATCH] sfc: extend the locking on mcdi->seqno

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Date:   Thu, 3 Mar 2022 08:12:32 +0000
From:   Martin Habets <habetsm.xilinx@...il.com>
To:     Niels Dossche <dossche.niels@...il.com>
Cc:     netdev@...r.kernel.org, Edward Cree <ecree.xilinx@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH] sfc: extend the locking on mcdi->seqno

On Tue, Mar 01, 2022 at 11:28:22PM +0100, Niels Dossche wrote:
> seqno could be read as a stale value outside of the lock. The lock is
> already acquired to protect the modification of seqno against a possible
> race condition. Place the reading of this value also inside this locking
> to protect it against a possible race condition.
> 
> Signed-off-by: Niels Dossche <dossche.niels@...il.com>

Acked-by: Martin Habets <habetsm.xilinx@...il.com>

> ---
>  drivers/net/ethernet/sfc/mcdi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/sfc/mcdi.c b/drivers/net/ethernet/sfc/mcdi.c
> index be6bfd6b7ec7..50baf62b2cbc 100644
> --- a/drivers/net/ethernet/sfc/mcdi.c
> +++ b/drivers/net/ethernet/sfc/mcdi.c
> @@ -163,9 +163,9 @@ static void efx_mcdi_send_request(struct efx_nic *efx, unsigned cmd,
>  	/* Serialise with efx_mcdi_ev_cpl() and efx_mcdi_ev_death() */
>  	spin_lock_bh(&mcdi->iface_lock);
>  	++mcdi->seqno;
> +	seqno = mcdi->seqno & SEQ_MASK;
>  	spin_unlock_bh(&mcdi->iface_lock);
>  
> -	seqno = mcdi->seqno & SEQ_MASK;
>  	xflags = 0;
>  	if (mcdi->mode == MCDI_MODE_EVENTS)
>  		xflags |= MCDI_HEADER_XFLAGS_EVREQ;
> -- 
> 2.35.1