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From: Thomas Gleixner <tglx@kernel.org>
To: Joe Damato <joe@dama.to>
Cc: intel-wired-lan@lists.osuosl.org, Tony Nguyen
 <anthony.l.nguyen@intel.com>, Przemek Kitszel
 <przemyslaw.kitszel@intel.com>, netdev@vger.kernel.org
Subject: Re: i40e: Fix preempt count leak in napi poll tracepoint
In-Reply-To: <aYpalNvTIiD4nym4@devvm20253.cco0.facebook.com>
References: <87v7g8zv2o.ffs@tglx>
 <aYpalNvTIiD4nym4@devvm20253.cco0.facebook.com>
Date: Mon, 09 Feb 2026 23:56:29 +0100
Message-ID: <87a4xhbk6a.ffs@tglx>
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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 ...