netdev - Re: [PATCH net] ipv4: igmp: hold wakelock to prevent delayed reports

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Date:   Mon, 04 Jun 2018 11:06:40 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     tejaswit@...eaurora.org
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net] ipv4: igmp: hold wakelock to prevent delayed
 reports

From: Tejaswi Tanikella <tejaswit@...eaurora.org>
Date: Fri, 1 Jun 2018 19:35:41 +0530

> On receiving a IGMPv2/v3 query, based on max_delay set in the header a
> timer is started to send out a response after a random time within
> max_delay. If the system then moves into suspend state, Report is
> delayed until system wakes up.
> 
> In one reported scenario, on arm64 devices, max_delay was set to 10s,
> Reports were consistantly delayed if the timer is scheduled after 5 plus
> seconds.
> 
> Hold wakelock while starting the timer to prevent moving into suspend
> state.
> 
> Signed-off-by: Tejaswi Tanikella <tejaswit@...eaurora.org>

As Florian stated, this won't be the only networking facility to hit
a problem like this.  So, if we go down this route, we probably want
to generically solve this.

But I have a deeper concern.

Do we really want every timer based querying mechanism to prevent a
system from being able to suspend?

We get to the point where external entities can generate traffic which
can prevent a remote system from entering suspend state.