linux-kernel - Re: [PATCH] Revert "net: linkwatch: add check for netdevice being present to linkwatch_do

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Date:   Thu, 24 Sep 2020 11:16:57 -0700
From:   Saeed Mahameed <saeed@...nel.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     David Miller <davem@...emloft.net>, hkallweit1@...il.com,
        geert+renesas@...der.be, f.fainelli@...il.com, andrew@...n.ch,
        gaku.inami.xh@...esas.com, yoshihiro.shimoda.uh@...esas.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "net: linkwatch: add check for netdevice being
 present to linkwatch_do_dev"

On Thu, 2020-09-24 at 09:03 -0700, Jakub Kicinski wrote:
> On Wed, 23 Sep 2020 22:49:37 -0700 Saeed Mahameed wrote:
> > 2) Another problematic scenario which i see is repeated in many
> > drivers:
> > 
> > shutdown/suspend()
> >     rtnl_lock()
> >     netif_device_detach()//Mark !present;
> >     stop()->carrier_off()->linkwatch_event()
> >     // at this point device is still IFF_UP and !present
> >     // due to the early detach above..  
> >     rtnl_unlock();
> 
> Maybe we can solve this by providing drivers with a better helper for
> the suspend use case?
> 
> AFAIU netif_device_detach() is used by both IO errors and drivers
> willingly detaching the device during normal operation (e.g. for
> suspend).
> 
> Since the suspend path can sleep if we have a separate helper perhaps
> we could fire off the appropriate events synchronously, and
> quiescence
> the stack properly?

I was thinking something similar, a more heavy
weight netif_device_detach(), which will be used in all drivers suspend
flows.
 
1) clear IFF_UP
2) ndo_stop()
3) fire events
4) mark !present
...

5) suspend device


but went and sampled some drivers and found there are many variations
for using netif_device_detach it is not going to be a simple task.