netdev - Re: [PATCH net 1/1] ionic: wait on queue start until after IFF

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Date:   Tue, 9 Jun 2020 12:51:17 -0700
From:   Shannon Nelson <snelson@...sando.io>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net 1/1] ionic: wait on queue start until after IFF_UP

On 6/9/20 12:47 PM, David Miller wrote:
> From: Shannon Nelson <snelson@...sando.io>
> Date: Mon,  8 Jun 2020 20:41:43 -0700
>
>> The netif_running() test looks at __LINK_STATE_START which
>> gets set before ndo_open() is called, there is a window of
>> time between that and when the queues are actually ready to
>> be run.  If ionic_check_link_status() notices that the link is
>> up very soon after netif_running() becomes true, it might try
>> to run the queues before they are ready, causing all manner of
>> potential issues.  Since the netdev->flags IFF_UP isn't set
>> until after ndo_open() returns, we can wait for that before
>> we allow ionic_check_link_status() to start the queues.
>>
>> On the way back to close, __LINK_STATE_START is cleared before
>> calling ndo_stop(), and IFF_UP is cleared after.  Both of
>> these need to be true in order to safely stop the queues
>> from ionic_check_link_status().
>>
>> Fixes: 49d3b493673a ("ionic: disable the queues on link down")
>> Signed-off-by: Shannon Nelson <snelson@...sando.io>
> What will make sure the queues actually get started if this
> event's queue start gets skipped in this scenerio?
>
> This code is only invoked when the link status changes or
> when the firmware is started.

If the link is already seen as up before ionic_open() is called it 
starts the queues at that point.

If link isn't seen until after ionic_open(), then the queues are started 
in this periodic link check.

sln