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

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Message-ID: <20210208120115.0372cbd7@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 8 Feb 2021 12:01:15 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Edwin Peer <edwin.peer@...adcom.com>
Cc:     netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        Andrew Gospodarek <andrew.gospodarek@...adcom.com>,
        Michael Chan <michael.chan@...adcom.com>
Subject: Re: [PATCH net] net: watchdog: hold device global xmit lock during
 tx disable

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 <edwin.peer@...adcom.com>

Reviewed-by: Jakub Kicinski <kuba@...nel.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.