netdev - Re: [PATCH net] be2net: Synchronize be_update_queues with dev

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Date:   Fri, 19 Jul 2019 14:26:52 +0900
From:   Benjamin Poirier <bpoirier@...e.com>
To:     Florian Fainelli <f.fainelli@...il.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>,
        Firo Yang <firo.yang@...e.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net] be2net: Synchronize be_update_queues with
 dev_watchdog

On 2019/07/18 10:23, Florian Fainelli wrote:
> On 7/17/19 6:42 PM, Benjamin Poirier wrote:
> > As pointed out by Firo Yang, a netdev tx timeout may trigger just before an
> > ethtool set_channels operation is started. be_tx_timeout(), which dumps
> > some queue structures, is not written to run concurrently with
> > be_update_queues(), which frees/allocates those queues structures. Add some
> > synchronization between the two.
> > 
> > Message-id: <CH2PR18MB31898E033896F9760D36BFF288C90@...PR18MB3189.namprd18.prod.outlook.com>
> > Signed-off-by: Benjamin Poirier <bpoirier@...e.com>
> 
> Would not moving the netif_tx_disable() in be_close() further up in the
> function resolve that problem as well?

Thanks for your review Florian,

No, netif_tx_disable() doesn't provide mutual exclusion with
dev_watchdog(). You can have:

cpu0                               cpu1
\ dev_watchdog
       \ netif_tx_lock
              \ be_tx_timeout
                     ...
                                   \ be_set_channels
                                          \ be_update_queues
                                                 \ netif_carrier_off
                                                 \ netif_tx_disable
                                                 ...
                                                 \ be_clear_queues
                     still running in
                     be_tx_timeout(),
                     boom!