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

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Date:   Wed, 23 Sep 2020 13:49:35 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Saeed Mahameed <saeed@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Gaku Inami <gaku.inami.xh@...esas.com>,
        Yoshihiro Shimoda <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 18.09.2020 19:58, Saeed Mahameed wrote:
> On Tue, 2020-09-01 at 17:02 +0200, Geert Uytterhoeven wrote:
>> This reverts commit 124eee3f6955f7aa19b9e6ff5c9b6d37cb3d1e2c.
>>
>> Inami-san reported that this commit breaks bridge support in a Xen
>> environment, and that reverting it fixes this.
>>
>> During system resume, bridge ports are no longer enabled, as that
>> relies
>> on the receipt of the NETDEV_CHANGE notification.  This notification
>> is
>> not sent, as netdev_state_change() is no longer called.
>>
>> Note that the condition this commit intended to fix never existed
>> upstream, as the patch triggering it and referenced in the commit was
>> never applied upstream.  Hence I can confirm s2ram on r8a73a4/ape6evm
>> and sh73a0/kzm9g works fine before/after this revert.
>>
>> Reported-by Gaku Inami <gaku.inami.xh@...esas.com>
>> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
>> ---
>>  net/core/link_watch.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/core/link_watch.c b/net/core/link_watch.c
>> index 75431ca9300fb9c4..c24574493ecf95e6 100644
>> --- a/net/core/link_watch.c
>> +++ b/net/core/link_watch.c
>> @@ -158,7 +158,7 @@ static void linkwatch_do_dev(struct net_device
>> *dev)
>>  	clear_bit(__LINK_STATE_LINKWATCH_PENDING, &dev->state);
>>  
>>  	rfc2863_policy(dev);
>> -	if (dev->flags & IFF_UP && netif_device_present(dev)) {
>> +	if (dev->flags & IFF_UP) {
> 
> So with your issue the devices is both IFF_UP and !present ? how so ?
> I think you should look into that.
> 
> I am ok with removing the "dev present" check from here just because we
> shouldn't  be expecting IFF_UP && !present .. such thing must be a bug
> somewhere else.
> 
>>  		if (netif_carrier_ok(dev))
>>  			dev_activate(dev);
>>  		else
> 


In __dev_close_many() we call ndo_stop() whilst IFF_UP is still set.
ndo_stop() may detach the device and bring down the PHY, resulting in an
async link change event that calls dev_get_stats(). The latter call may
have a problem if the device is detached. In a first place I'd consider
such a case a network driver bug (ndo_get_stats/64 should check for
device presence if depending on it).
The additional check in linkwatch_do_dev() was meant to protect from such
driver issues.