netdev - Re: [PATCH net] net: fix race on decreasing number of TX queues

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Message-Id: <20180214.141613.66054944399992487.davem@davemloft.net>
Date:   Wed, 14 Feb 2018 14:16:13 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     jakub.kicinski@...ronome.com
Cc:     john.fastabend@...il.com, alexander.duyck@...il.com,
        tom@...bertland.com, netdev@...r.kernel.org,
        oss-drivers@...ronome.com
Subject: Re: [PATCH net] net: fix race on decreasing number of TX queues

From: Jakub Kicinski <jakub.kicinski@...ronome.com>
Date: Mon, 12 Feb 2018 21:35:31 -0800

> netif_set_real_num_tx_queues() can be called when netdev is up.
> That usually happens when user requests change of number of
> channels/rings with ethtool -L.  The procedure for changing
> the number of queues involves resetting the qdiscs and setting
> dev->num_tx_queues to the new value.  When the new value is
> lower than the old one, extra care has to be taken to ensure
> ordering of accesses to the number of queues vs qdisc reset.
> 
> Currently the queues are reset before new dev->num_tx_queues
> is assigned, leaving a window of time where packets can be
> enqueued onto the queues going down, leading to a likely
> crash in the drivers, since most drivers don't check if TX
> skbs are assigned to an active queue.
> 
> Fixes: e6484930d7c7 ("net: allocate tx queues in register_netdevice")
> Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
> ---
> Also reported: http://lists.openwall.net/netdev/2017/04/26/211,
> GSO just made it more likely.

Looks good, applied and queued up for -stable, thanks!