netdev - [PATCH net-next 2/3] net: napi: use READ_ONCE()/WRITE

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Message-Id: <20200422161329.56026-3-edumazet@google.com>
Date:   Wed, 22 Apr 2020 09:13:28 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Luigi Rizzo <lrizzo@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH net-next 2/3] net: napi: use READ_ONCE()/WRITE_ONCE()

gro_flush_timeout and napi_defer_hard_irqs can be read
from napi_complete_done() while other cpus write the value,
whithout explicit synchronization.

Use READ_ONCE()/WRITE_ONCE() to annotate the races.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/core/dev.c       | 6 +++---
 net/core/net-sysfs.c | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 67585484ad32b698c6bc4bf17f5d87c345d77502..afff16849c261181b4f1043cf3d23627c75c7898 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6242,12 +6242,12 @@ bool napi_complete_done(struct napi_struct *n, int work_done)
 
 	if (work_done) {
 		if (n->gro_bitmask)
-			timeout = n->dev->gro_flush_timeout;
-		n->defer_hard_irqs_count = n->dev->napi_defer_hard_irqs;
+			timeout = READ_ONCE(n->dev->gro_flush_timeout);
+		n->defer_hard_irqs_count = READ_ONCE(n->dev->napi_defer_hard_irqs);
 	}
 	if (n->defer_hard_irqs_count > 0) {
 		n->defer_hard_irqs_count--;
-		timeout = n->dev->gro_flush_timeout;
+		timeout = READ_ONCE(n->dev->gro_flush_timeout);
 		if (timeout)
 			ret = false;
 	}
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index f3b650cd09231fd99604f6f66bab454eabaa06be..880e89c894f6f3669b132547926164c1f36fc986 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -367,7 +367,7 @@ NETDEVICE_SHOW_RW(tx_queue_len, fmt_dec);
 
 static int change_gro_flush_timeout(struct net_device *dev, unsigned long val)
 {
-	dev->gro_flush_timeout = val;
+	WRITE_ONCE(dev->gro_flush_timeout, val);
 	return 0;
 }
 
@@ -384,7 +384,7 @@ NETDEVICE_SHOW_RW(gro_flush_timeout, fmt_ulong);
 
 static int change_napi_defer_hard_irqs(struct net_device *dev, unsigned long val)
 {
-	dev->napi_defer_hard_irqs = val;
+	WRITE_ONCE(dev->napi_defer_hard_irqs, val);
 	return 0;
 }
 
-- 
2.26.1.301.g55bc3eb7cb9-goog