linux-kernel - [PATCH v3 4/8] xen/netback: fix spurious event detection for common event case

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Date:   Fri, 19 Feb 2021 16:40:26 +0100
From:   Juergen Gross <jgross@...e.com>
To:     xen-devel@...ts.xenproject.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Juergen Gross <jgross@...e.com>, Wei Liu <wei.liu@...nel.org>,
        Paul Durrant <paul@....org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, stable@...r.kernel.org,
        Jan Beulich <jbeulich@...e.com>, Wei Liu <wl@....org>
Subject: [PATCH v3 4/8] xen/netback: fix spurious event detection for common event case

In case of a common event for rx and tx queue the event should be
regarded to be spurious if no rx and no tx requests are pending.

Unfortunately the condition for testing that is wrong causing to
decide a event being spurious if no rx OR no tx requests are
pending.

Fix that plus using local variables for rx/tx pending indicators in
order to split function calls and if condition.

Cc: stable@...r.kernel.org
Fixes: 23025393dbeb3b ("xen/netback: use lateeoi irq binding")
Signed-off-by: Juergen Gross <jgross@...e.com>
Reviewed-by: Jan Beulich <jbeulich@...e.com>
Reviewed-by: Paul Durrant <paul@....org>
Reviewed-by: Wei Liu <wl@....org>
---
V2:
- new patch, fixing FreeBSD performance issue
---
 drivers/net/xen-netback/interface.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index acb786d8b1d8..e02a4fbb74de 100644
--- 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);
 	}
-- 
2.26.2