linux-kernel - Re: [PATCH 6.6 3/3] net: Allow to use SMP threads for backlog NAPI.

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Message-ID: <2026012039-shuffle-apple-43ec@gregkh>
Date: Tue, 20 Jan 2026 10:21:58 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Jakub Kicinski <kuba@...nel.org>, wen.yang@...ux.dev,
	stable@...r.kernel.org, linux-kernel@...r.kernel.org,
	Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH 6.6 3/3] net: Allow to use SMP threads for backlog NAPI.

On Tue, Jan 20, 2026 at 09:01:04AM +0100, Sebastian Andrzej Siewior wrote:
> On 2026-01-20 07:03:58 [+0100], Greg Kroah-Hartman wrote:
> > On Mon, Jan 19, 2026 at 05:30:26PM +0100, Sebastian Andrzej Siewior wrote:
> > > On 2026-01-19 08:25:34 [-0800], Jakub Kicinski wrote:
> > > > On Mon, 19 Jan 2026 00:15:46 +0800 wen.yang@...ux.dev wrote:
> > > > > From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> > > > > 
> > > > > commit dad6b97702639fba27a2bd3e986982ad6f0db3a7 upstream.
> > > > > 
> > > > > Backlog NAPI is a per-CPU NAPI struct only (with no device behind it)
> > > > > used by drivers which don't do NAPI them self, RPS and parts of the
> > > > > stack which need to avoid recursive deadlocks while processing a packet.
> > > > 
> > > > This is a rather large change to backport into LTS.
> > > 
> > > I agree. While I saw these patches flying by, I don't remember a mail
> > > where it was justified why it was needed. Did I miss it?
> > 
> > Please see patch 0/3 in this series:
> > 	https://lore.kernel.org/all/cover.1768751557.git.wen.yang@linux.dev/
> 
> The reasoning why this is needed is due to PREEMPT_RT. This targets v6.6
> and PREEMPT_RT is officially supported upstream since v6.12. For v6.6
> you still need the out-of-tree patch. This means not only select the
> Kconfig symbol but also a bit futex, ptrace or printk. This queue does
> not include the three patches here but has another workaround having
> more or less the same effect.
> 
> If this is needed only for PREEMPT_RT's sake I would suggest to route it
> via the stable-rt instead and replace what is currently there.

It's already merged, should this be reverted?  I forgot RT was only for
6.12 and newer, sorry.

greg k-h