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Mon, 09 Feb 2026 14:07:17 -0800 (PST) Date: Mon, 9 Feb 2026 14:07:16 -0800 From: Joe Damato To: Thomas Gleixner Cc: intel-wired-lan@lists.osuosl.org, Tony Nguyen , Przemek Kitszel , netdev@vger.kernel.org Subject: Re: i40e: Fix preempt count leak in napi poll tracepoint Message-ID: Mail-Followup-To: Joe Damato , Thomas Gleixner , intel-wired-lan@lists.osuosl.org, Tony Nguyen , Przemek Kitszel , netdev@vger.kernel.org References: <87v7g8zv2o.ffs@tglx> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87v7g8zv2o.ffs@tglx> 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. > Use smp_processor_id() instead. Thanks. > Fixes: 6d4d584a7ea8 ("i40e: Add i40e_napi_poll tracepoint") > Signed-off-by: Thomas Gleixner > Cc: Tony Nguyen > Cc: Przemek Kitszel > Cc: intel-wired-lan@lists.osuosl.org > Cc: netdev@vger.kernel.org > --- > drivers/net/ethernet/intel/i40e/i40e_trace.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > --- a/drivers/net/ethernet/intel/i40e/i40e_trace.h > +++ b/drivers/net/ethernet/intel/i40e/i40e_trace.h > @@ -88,7 +88,7 @@ TRACE_EVENT(i40e_napi_poll, > __entry->rx_clean_complete = rx_clean_complete; > __entry->tx_clean_complete = tx_clean_complete; > __entry->irq_num = q->irq_num; > - __entry->curr_cpu = get_cpu(); > + __entry->curr_cpu = smp_processor_id(); > __assign_str(qname); > __assign_str(dev_name); > __assign_bitmask(irq_affinity, cpumask_bits(&q->affinity_mask), > Reviewed-by: Joe Damato