linux-kernel - Re: [PATCH 4.19 044/321] mac80211: fix station inactive

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Date:   Wed, 04 Dec 2019 13:05:23 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Pavel Machek <pavel@...x.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Ahmed Zaki <anzaki@...il.com>, Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 044/321] mac80211: fix station inactive_time
 shortly after boot

On Wed, 2019-12-04 at 11:56 +0000, Pavel Machek wrote:
 
> > -	if (time_after(stats->last_rx, sta->status_stats.last_ack))
> > +	if (!sta->status_stats.last_ack ||
> > +	    time_after(stats->last_rx, sta->status_stats.last_ack))
> >  		return stats->last_rx;
> >  	return sta->status_stats.last_ack;
> >  }
> 
> I mean, jiffies do wrapraound periodically, so eventually we'll have
> sta->status_stats.last_ack == 0 even through it is not short after
> boot, no?

Yeah. I contemplated that when I applied the original patch - it's a bit
complicated otherwise, you have to track "is this valid" etc.

Since this is updated on pretty much every frame, it's highly unlikely
you'll go without the value for long, so I figured this was good enough.

johannes