[PATCH net] net: watchdog: hold device global xmit lock during tx disable

Prevent netif_tx_disable() running concurrently with dev_watchdog() by
taking the device global xmit lock. Otherwise, the recommended:

	netif_carrier_off(dev);
	netif_tx_disable(dev);

driver shutdown sequence can happen after the watchdog has already
checked carrier, resulting in possible false alarms. This is because
netif_tx_lock() only sets the frozen bit without maintaining the locks
on the individual queues.

Fixes: c3f26a269c24 ("netdev: Fix lockdep warnings in multiqueue configurations.")
Signed-off-by: Edwin Peer <redacted>
---
 include/linux/netdevice.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 259be67644e3..5ff27c12ce68 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h

@@ -4352,6 +4352,7 @@ static inline void netif_tx_disable(struct net_device *dev)
 
 	local_bh_disable();
 	cpu = smp_processor_id();
+	spin_lock(&dev->tx_global_lock);
 	for (i = 0; i < dev->num_tx_queues; i++) {
 		struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
 

@@ -4359,6 +4360,7 @@ static inline void netif_tx_disable(struct net_device *dev)
 		netif_tx_stop_queue(txq);
 		__netif_tx_unlock(txq);
 	}
+	spin_unlock(&dev->tx_global_lock);
 	local_bh_enable();
 }
 

-- 
2.30.0

On Fri,  5 Feb 2021 17:37:32 -0800 Edwin Peer wrote:

Prevent netif_tx_disable() running concurrently with dev_watchdog() by
taking the device global xmit lock. Otherwise, the recommended:

	netif_carrier_off(dev);
	netif_tx_disable(dev);

driver shutdown sequence can happen after the watchdog has already
checked carrier, resulting in possible false alarms. This is because
netif_tx_lock() only sets the frozen bit without maintaining the locks
on the individual queues.

Fixes: c3f26a269c24 ("netdev: Fix lockdep warnings in multiqueue configurations.")
Signed-off-by: Edwin Peer <redacted>

Reviewed-by: Jakub Kicinski <kuba@kernel.org>

Even though using the dev->tx_global_lock as a barrier is not very
clean in itself the thinking is that this restores previous semantics
with deeper changes.

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Fri,  5 Feb 2021 17:37:32 -0800 you wrote:

Prevent netif_tx_disable() running concurrently with dev_watchdog() by
taking the device global xmit lock. Otherwise, the recommended:

	netif_carrier_off(dev);
	netif_tx_disable(dev);

driver shutdown sequence can happen after the watchdog has already
checked carrier, resulting in possible false alarms. This is because
netif_tx_lock() only sets the frozen bit without maintaining the locks
on the individual queues.

[...]

Here is the summary with links:
  - [net] net: watchdog: hold device global xmit lock during tx disable
    https://git.kernel.org/netdev/net/c/3aa6bce9af0e

You are awesome, thank you!
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