netdev - [PATCH net-next 1/4] net: use an atomic_long_t for queue->trans

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Message-Id: <20211117032924.1740327-2-eric.dumazet@gmail.com>
Date:   Tue, 16 Nov 2021 19:29:21 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        david decotigny <david.decotigny@...gle.com>
Subject: [PATCH net-next 1/4] net: use an atomic_long_t for queue->trans_timeout

From: Eric Dumazet <edumazet@...gle.com>

tx_timeout_show() assumed dev_watchdog() would stop all
the queues, to fetch queue->trans_timeout under protection
of the queue->_xmit_lock.

As we want to no longer disrupt transmits, we use an
atomic_long_t instead.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: david decotigny <david.decotigny@...gle.com>
---
 include/linux/netdevice.h | 2 +-
 net/core/net-sysfs.c      | 6 +-----
 net/sched/sch_generic.c   | 2 +-
 3 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 31a7e6b2768123021690a3dc8572c5e8cb0e0027..143ac02c7f1cc90cf6704574fb0012e1ba830c70 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -592,7 +592,7 @@ struct netdev_queue {
 	 * Number of TX timeouts for this queue
 	 * (/sys/class/net/DEV/Q/trans_timeout)
 	 */
-	unsigned long		trans_timeout;
+	atomic_long_t		trans_timeout;
 
 	/* Subordinate device that the queue has been assigned to */
 	struct net_device	*sb_dev;
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 9c01c642cf9ef384fe54e56243b102ef838d0a62..addbef5419fbb62ce83f5132ae21c9d2872e95f5 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1201,11 +1201,7 @@ static const struct sysfs_ops netdev_queue_sysfs_ops = {
 
 static ssize_t tx_timeout_show(struct netdev_queue *queue, char *buf)
 {
-	unsigned long trans_timeout;
-
-	spin_lock_irq(&queue->_xmit_lock);
-	trans_timeout = queue->trans_timeout;
-	spin_unlock_irq(&queue->_xmit_lock);
+	unsigned long trans_timeout = atomic_long_read(&queue->trans_timeout);
 
 	return sprintf(buf, fmt_ulong, trans_timeout);
 }
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 3b0f620958037eb46e395f172c2315fdd98be914..1b4328bd495d54d44a9d51b53c8e8bc18b9cc294 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -467,7 +467,7 @@ static void dev_watchdog(struct timer_list *t)
 				    time_after(jiffies, (trans_start +
 							 dev->watchdog_timeo))) {
 					some_queue_timedout = 1;
-					txq->trans_timeout++;
+					atomic_long_inc(&txq->trans_timeout);
 					break;
 				}
 			}
-- 
2.34.0.rc1.387.gb447b232ab-goog