netdev - Re: [PATCH net] sch_netem: acquire qdisc lock in netem

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Message-ID: <CANn89iJ6qHJC9NZx-u9Mm6am3OVNPP2u2xjpmUspDaAnq3Sh3w@mail.gmail.com>
Date: Thu, 22 Jun 2023 18:31:37 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: patchwork-bot+netdevbpf@...nel.org
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, 
	netdev@...r.kernel.org, eric.dumazet@...il.com, syzkaller@...glegroups.com, 
	stephen@...workplumber.org, jhs@...atatu.com, xiyou.wangcong@...il.com, 
	jiri@...nulli.us
Subject: Re: [PATCH net] sch_netem: acquire qdisc lock in netem_change()

On Thu, Jun 22, 2023 at 11:20 AM <patchwork-bot+netdevbpf@...nel.org> wrote:
>
> Hello:
>
> This patch was applied to netdev/net.git (main)
> by Paolo Abeni <pabeni@...hat.com>:
>
> On Tue, 20 Jun 2023 18:44:25 +0000 you wrote:
> > syzbot managed to trigger a divide error [1] in netem.
> >
> > It could happen if q->rate changes while netem_enqueue()
> > is running, since q->rate is read twice.
> >
> > It turns out netem_change() always lacked proper synchronization.
> >
> > [...]
>
> Here is the summary with links:
>   - [net] sch_netem: acquire qdisc lock in netem_change()
>     https://git.kernel.org/netdev/net/c/2174a08db80d
>
> You are awesome, thank you!
> --
> Deet-doot-dot, I am a bot.
> https://korg.docs.kernel.org/patchwork/pwbot.html

I missed the fact that get_dist_table() was called from netem_change()

This function uses GFP_KERNEL and also acquires the qdisc lock.

I will send a fix soon.