linux-kernel - Re: [PATCH v2 4/8] xen/netback: fix spurious event detection for common event case

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Date:   Thu, 11 Feb 2021 11:53:17 +0100
From:   Jan Beulich <jbeulich@...e.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     Wei Liu <wei.liu@...nel.org>, Paul Durrant <paul@....org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        xen-devel@...ts.xenproject.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/8] xen/netback: fix spurious event detection for
 common event case

On 11.02.2021 11:16, Juergen Gross wrote:
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -162,13 +162,15 @@ irqreturn_t xenvif_interrupt(int irq, void *dev_id)
>  {
>  	struct xenvif_queue *queue = dev_id;
>  	int old;
> +	bool has_rx, has_tx;
>  
>  	old = atomic_fetch_or(NETBK_COMMON_EOI, &queue->eoi_pending);
>  	WARN(old, "Interrupt while EOI pending\n");
>  
> -	/* Use bitwise or as we need to call both functions. */
> -	if ((!xenvif_handle_tx_interrupt(queue) |
> -	     !xenvif_handle_rx_interrupt(queue))) {
> +	has_tx = xenvif_handle_tx_interrupt(queue);
> +	has_rx = xenvif_handle_rx_interrupt(queue);
> +
> +	if (!has_rx && !has_tx) {
>  		atomic_andnot(NETBK_COMMON_EOI, &queue->eoi_pending);
>  		xen_irq_lateeoi(irq, XEN_EOI_FLAG_SPURIOUS);
>  	}
> 

Ah yes, what was originally meant really was

	if (!(xenvif_handle_tx_interrupt(queue) |
	      xenvif_handle_rx_interrupt(queue))) {

(also hinted at by the otherwise pointless inner parentheses),
which you simply write in an alternative way.

Reviewed-by: Jan Beulich <jbeulich@...e.com>

Jan