netdev - Re: [PATCH net-next] net: Restore napi threaded state only when it is enabled

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAAywjhQN4Re3+64=qiukq1Q2wtLBj2pesaDSsvojK4tDAGHegw@mail.gmail.com>
Date: Tue, 22 Jul 2025 19:36:31 -0700
From: Samiullah Khawaja <skhawaja@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: "David S . Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Paolo Abeni <pabeni@...hat.com>, almasrymina@...gle.com, willemb@...gle.com, 
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: Restore napi threaded state only when it is enabled

On Tue, Jul 22, 2025 at 6:36 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Mon, 21 Jul 2025 23:36:08 +0000 Samiullah Khawaja wrote:
> > Commit 2677010e7793 ("Add support to set NAPI threaded for individual
> > NAPI") added support to enable/disable threaded napi using netlink. This
> > also extended the napi config save/restore functionality to set the napi
> > threaded state. This breaks the netdev reset when threaded napi is
>
> "This breaks the netdev reset" is very vague.
Basically on netdev reset inside napi_enable when it calls
napi_restore_config it tries to stop the NAPI kthread. Since during
napi_enable, the NAPI has STATE_SCHED set on it, the stop_kthread gets
stuck waiting for the STATE_SCHED to be unset. It should not be
destroying the kthread since threaded is enabled at device level. But
I think your point below is valid, we should probably set
napi->config->threaded in netif_set_threaded.

I should add this to the commit message.
>
> > enabled at device level as the napi_restore_config tries to stop the
> > kthreads as napi->config->thread is false when threaded is enabled at
> > device level.
>
> My reading of the commit message is that the WARN triggers, but
> looking at the code I think you mean that we fail to update the
> config when we set at the device level?
>
> > The napi_restore_config should only restore the napi threaded state when
> > threaded is enabled at NAPI level.
> >
> > The issue can be reproduced on virtio-net device using qemu. To
> > reproduce the issue run following,
> >
> >   echo 1 > /sys/class/net/threaded
> >   ethtool -L eth0 combined 1
>
> Maybe we should add that as a test under tools/testing/drivers/net -
> it will run against netdevsim but also all drivers we test which
> currently means virtio and fbnic, but hopefully soon more. Up to you.
+1

I do want to add a test for it. I was thinking of extending
nl_netdev.py but that doesn't seem suitable as it only looks at the
state. I will look at the driver directory. Should I send a test with
this fix or should I send that later after the next reopen?
>
> I'm not sure I agree with the semantics, tho. IIUC you're basically
> making the code prefer threaded option. If user enables threading
> for the device, then disables it for a NAPI - reconfiguration will
> lose the fact that specific NAPI instance was supposed to have threading
> disabled. Why not update napi->config in netif_set_threaded() instead?
I think this discrepancy is orthogonal to the stopping of threads in
restore. This is because the napi_enable is calling restore_config and
then setting the STATE_THREADED bit on napis based on dev->threaded.
Even if restore unsets the THREADED bit (which would have already been
unset during napi_disable), it will be set again based on
dev->threaded.

I think napi_restore_config should be called after setting up STATE bits?
> --
> pw-bot: cr