netdev - Re: i40e: Fix preempt count leak in napi poll tracepoint

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Message-ID: <aYqe20qJ9sKc30K3@MacBook-Air-2.local>
Date: Mon, 9 Feb 2026 18:58:35 -0800
From: Joe Damato <joe@...a.to>
To: Thomas Gleixner <tglx@...nel.org>
Cc: intel-wired-lan@...ts.osuosl.org,
	Tony Nguyen <anthony.l.nguyen@...el.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	netdev@...r.kernel.org
Subject: Re: i40e: Fix preempt count leak in napi poll tracepoint

On Tue, Feb 10, 2026 at 01:25:11AM +0100, Thomas Gleixner wrote:
> On Mon, Feb 09 2026 at 23:56, Thomas Gleixner wrote:
> > On Mon, Feb 09 2026 at 14:07, Joe Damato wrote:
> >
> >> On Sat, Feb 07, 2026 at 11:50:23AM +0100, Thomas Gleixner wrote:
> >>> Using get_cpu() in the tracepoint assignment causes an obvious preempt
> >>> count leak because nothing invokes put_cpu() to undo it:
> >>> 
> >>>   softirq: huh, entered softirq 3 NET_RX with preempt_count 00000100, exited with 00000101?
> >>> 
> >>> This clearly has seen a lot of testing in the last 3+ years...
> >>
> >> I'm the author who introduced the bug. FWIW, I did use it quite a bit when I
> >> had i40e devices.
> >
> > Right, but always with PREEMPT_NONE and no debug option which would
> > enforce PREEMPT_COUNT ...
> 
> Forgot to mention that's what is required before submitting patches
> according to Documentation/process/submit-checklist.rst

This is a very helpful reply, thanks!

> But who cares about documentation aside of the people who write it?

I've written a lot of documentation, too, but sometimes people just make
mistakes.

- Joe