netdev - Re: [PATCH net] be2net: Signal that the device cannot transmit during reconfiguration

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Message-ID: <20190717082340.GA6015@f1>
Date:   Wed, 17 Jul 2019 17:23:40 +0900
From:   Benjamin Poirier <bpoirier@...e.com>
To:     Firo Yang <firo.yang@...e.com>
Cc:     David Miller <davem@...emloft.net>,
        Ajit Khaparde <ajit.khaparde@...adcom.com>,
        Sathya Perla <sathya.perla@...adcom.com>,
        Somnath Kotur <somnath.kotur@...adcom.com>,
        Sriharsha Basavapatna <sriharsha.basavapatna@...adcom.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net] be2net: Signal that the device cannot transmit
 during reconfiguration

On 2019/07/17 13:23, Firo Yang wrote:
> I think there is a problem if dev_watchdog() is triggered before netif_carrier_off(). dev_watchdog() might call ->ndo_tx_timeout(), i.e. be_tx_timeout(), if txq timeout  happens. Thus be_tx_timeout() could still be able to access the memory which is being freed by be_update_queues().

Good point. That's a separate problem which would occur in case of real
tx timeout. How about this followup change:

--- a/drivers/net/ethernet/emulex/benet/be_main.c
+++ b/drivers/net/ethernet/emulex/benet/be_main.c
@@ -4698,8 +4698,13 @@ int be_update_queues(struct be_adapter *adapter)
 	int status;
 
 	if (netif_running(netdev)) {
+		/* be_tx_timeout() must not run concurrently with this
+		 * function, synchronize with an already-running dev_watchdog
+		 */
+		netif_tx_lock_bh(netdev);
 		/* device cannot transmit now, avoid dev_watchdog timeouts */
 		netif_carrier_off(netdev);
+		netif_tx_unlock_bh(netdev);
 
 		be_close(netdev);
 	}