[PATCH net] net: do not acquire dev->tx_global_lock in netdev_watchdog_up()

[PATCH net] net: do not acquire dev->tx_global_lock in netdev_watchdog_up()

[Eric Dumazet]

Marek Szyprowski reported a deadlock during system resume when virtio_net
driver is used.

The deadlock occurs because netif_device_attach() is called while holding
dev->tx_global_lock (via netif_tx_lock_bh() in virtnet_restore_up()).
netif_device_attach() calls __netdev_watchdog_up(), which now also tries
to acquire dev->tx_global_lock to synchronize with dev_watchdog().

This recursive lock acquisition results in a deadlock.

Fix this by removing the tx_global_lock acquisition from netdev_watchdog_up().

The critical state (watchdog_timer and watchdog_ref_held) is already
protected by dev->watchdog_lock, which was introduced in the blamed commit.

Fixes: 8eed5519e496 ("net: watchdog: fix refcount tracking races")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Closes: https://lore.kernel.org/netdev/a443376e-5187-4268-93b3-58047ef113a8@samsung.com/
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
---
 net/sched/sch_generic.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 3f1c510df850dbdbaf10d483547c7b1f3a5d5482..ef2b4bf51564173751c74fefe17e3913ed2fa056 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -594,9 +594,8 @@ void netdev_watchdog_up(struct net_device *dev)
 		return;
 	if (dev->watchdog_timeo <= 0)
 		dev->watchdog_timeo = 5*HZ;
-	spin_lock_bh(&dev->tx_global_lock);
 
-	spin_lock(&dev->watchdog_lock);
+	spin_lock_bh(&dev->watchdog_lock);
 	if (!mod_timer(&dev->watchdog_timer,
 		       round_jiffies(jiffies + dev->watchdog_timeo))) {
 		if (!dev->watchdog_ref_held) {
@@ -605,9 +604,7 @@ void netdev_watchdog_up(struct net_device *dev)
 			dev->watchdog_ref_held = true;
 		}
 	}
-	spin_unlock(&dev->watchdog_lock);
-
-	spin_unlock_bh(&dev->tx_global_lock);
+	spin_unlock_bh(&dev->watchdog_lock);
 }
 EXPORT_SYMBOL_GPL(netdev_watchdog_up);
 
-- 
2.55.0.rc0.786.g65d90a0328-goog

Re: [PATCH net] net: do not acquire dev->tx_global_lock in netdev_watchdog_up()

[Simon Horman]

On Mon, Jun 22, 2026 at 11:01:08AM +0000, Eric Dumazet wrote:
> Marek Szyprowski reported a deadlock during system resume when virtio_net
> driver is used.
> 
> The deadlock occurs because netif_device_attach() is called while holding
> dev->tx_global_lock (via netif_tx_lock_bh() in virtnet_restore_up()).
> netif_device_attach() calls __netdev_watchdog_up(), which now also tries
> to acquire dev->tx_global_lock to synchronize with dev_watchdog().
> 
> This recursive lock acquisition results in a deadlock.
> 
> Fix this by removing the tx_global_lock acquisition from netdev_watchdog_up().
> 
> The critical state (watchdog_timer and watchdog_ref_held) is already
> protected by dev->watchdog_lock, which was introduced in the blamed commit.
> 
> Fixes: 8eed5519e496 ("net: watchdog: fix refcount tracking races")
> Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Closes: https://lore.kernel.org/netdev/a443376e-5187-4268-93b3-58047ef113a8@samsung.com/
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>

Reviewed-by: Simon Horman <horms@kernel.org>

Re: [PATCH net] net: do not acquire dev->tx_global_lock in netdev_watchdog_up()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Mon, 22 Jun 2026 11:01:08 +0000 you wrote:
> Marek Szyprowski reported a deadlock during system resume when virtio_net
> driver is used.
> 
> The deadlock occurs because netif_device_attach() is called while holding
> dev->tx_global_lock (via netif_tx_lock_bh() in virtnet_restore_up()).
> netif_device_attach() calls __netdev_watchdog_up(), which now also tries
> to acquire dev->tx_global_lock to synchronize with dev_watchdog().
> 
> [...]

Here is the summary with links:
  - [net] net: do not acquire dev->tx_global_lock in netdev_watchdog_up()
    https://git.kernel.org/netdev/net/c/d09a78a2a469

You are awesome, thank you!
-- 
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