From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 3A3A03612F8; Tue, 18 Aug 2026 07:31:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787038304; cv=none; b=EU/UAzsDtSM7MSXRa2cg4iBEAdjZDCOXOb6ZZ5chCvudEGtXo+dbSwrXcIdi02OLXKfOmsKySs+JoA6NVe9QcQqtnoa3kQfjdvKRVh9B2Ae1p9f4yhoy4ufZsDGqGs0DCY4ML0HKAVaIjED2TkmwfGM++h9O3AbaZ0eNltUcBFg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787038304; c=relaxed/simple; bh=qQc7NpVgjlwCgtPxFyKMVtz15dITF6AD/7Wy6HDmHxk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=kD5PEf0TugFqoFR3N1iaNRgZD+Brx9BDxJEkBjBc3fyt/fHy4RvVVFBwOOmHE5WN6wpsunp069W3x3MAxxwLNeB01YcqUkVc3OH+R6sI5RMGu2x8shfpEnlwyJ7I0rCWy9OeLbFIG/wHdD23XRSKpvlK+9wFlDCZtdjD/sVLwMQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=q2nGwtoA; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="q2nGwtoA" Received: from [192.168.1.70] (unknown [4.194.122.170]) by linux.microsoft.com (Postfix) with ESMTPSA id D85D320B7167; Tue, 18 Aug 2026 00:30:56 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com D85D320B7167 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1787038264; bh=33oeJJ2KUl0c85m92fbwyfbJQ2UNWDvCfDyVxz5S2j4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=q2nGwtoAukCeLTzPxYYr6c23vKRkqtZ52Zjv8TzRZkwl0RZcW+uz/1MQsshivtqzA G4TbUr4MlTAM6k/PMNhqsT6NomohtocqNCFggsiDNe7vpsm0fsRI5FiVgclObAIXY0 jjRQQ3oplBqjyFIBME3El7DBVd5mSjwTMtO7zpaw= Message-ID: <72ccf7d4-0fda-4f55-a47c-27486ef3e159@linux.microsoft.com> Date: Tue, 18 Aug 2026 13:01:20 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/3] x86/irq: Use irq_chip_retrigger_hierarchy() in fixup_irqs() To: Michael Kelley , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "x86@kernel.org" , "Joerg Roedel (AMD)" , Will Deacon , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Long Li , Lorenzo Pieralisi , =?UTF-8?Q?Krzysztof_Wilczy=C5=84ski?= , Manivannan Sadhasivam , Bjorn Helgaas Cc: "H. Peter Anvin" , Suravee Suthikulpanit , Vasant Hegde , Robin Murphy , Rob Herring , Shradha Gupta , Aditya Garg , "iommu@lists.linux.dev" , "linux-hyperv@vger.kernel.org" , "linux-pci@vger.kernel.org" , "linux-kernel@vger.kernel.org" References: <20260810090716.2325295-1-namjain@linux.microsoft.com> <20260810090716.2325295-3-namjain@linux.microsoft.com> Content-Language: en-US From: Naman Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 8/18/2026 10:40 AM, Michael Kelley wrote: > From: Naman Jain Sent: Monday, August 10, 2026 2:07 AM >> >> fixup_irqs() re-injects a pending interrupt on its new target CPU by >> looking at the outermost domain chip and invoking its irq_retrigger() >> callback directly. That only works when the outermost chip happens to >> install an irq_retrigger() callback, which is not guaranteed for every >> irqchip and could lead to lost interrupts on CPU hot-unplug. >> >> Use irq_chip_retrigger_hierarchy() instead, which walks up the interrupt >> hierarchy until it finds a chip that implements irq_retrigger(). >> >> While at it, move the loop-local variables into the loop scope and use a >> scoped guard for desc->lock. > > Moving the loop-local variables into the loop scope seems to be churn > with no real benefit. I know Thomas' suggested code made that change > and he's the maintainer, so it's his call. But still . . . > > Changing to use the scoped guard seems OK since that's a new pattern > we want to be using. > I can avoid moving this to loop-local variable in next version, if we are moving ahead with changing the logic for below comments. >> >> VECTOR_RETRIGGERED is now set only when the retrigger succeeds >> (irq_chip_retrigger_hierarchy() returns non-zero) instead of >> unconditionally. This is harmless today since apic_retrigger_irq() >> always returns 1, and arguably more correct. No functional change >> intended for chips which already provide an irq_retrigger() callback >> on the outermost domain. >> >> Suggested-by: Thomas Gleixner >> Reviewed-by: Shradha Gupta >> Signed-off-by: Naman Jain >> --- >> arch/x86/kernel/irq.c | 23 +++++++---------------- >> 1 file changed, 7 insertions(+), 16 deletions(-) >> >> diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c >> index 30122f0b3af96..ef1bdd3c4659a 100644 >> --- a/arch/x86/kernel/irq.c >> +++ b/arch/x86/kernel/irq.c >> @@ -466,11 +466,6 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_posted_msi_notification) >> /* A cpu has been removed from cpu_online_mask. Reset irq affinities. */ >> void fixup_irqs(void) >> { >> - unsigned int vector; >> - struct irq_desc *desc; >> - struct irq_data *data; >> - struct irq_chip *chip; >> - >> irq_migrate_all_off_this_cpu(); >> >> /* >> @@ -489,22 +484,18 @@ void fixup_irqs(void) >> * vector_lock because the cpu is already marked !online, so >> * nothing else will touch it. >> */ >> - for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS; vector++) { >> - if (IS_ERR_OR_NULL(__this_cpu_read(vector_irq[vector]))) >> + for (unsigned int vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS; vector++) { >> + struct irq_desc *desc = __this_cpu_read(vector_irq[vector]); >> + >> + if (IS_ERR_OR_NULL(desc)) >> continue; >> >> if (is_vector_pending(vector)) { >> - desc = __this_cpu_read(vector_irq[vector]); >> - >> - raw_spin_lock(&desc->lock); >> - data = irq_desc_get_irq_data(desc); >> - chip = irq_data_get_irq_chip(data); >> - if (chip->irq_retrigger) { >> - chip->irq_retrigger(data); >> + guard(raw_spinlock)(&desc->lock); >> + if (irq_chip_retrigger_hierarchy(&desc->irq_data)) > > The existing code uses irq_desc_get_irq_data() instead of directly > accessing the irq_data field. I *think* using the function is preferred, > but maybe I'm out-of-date. I can switch to irq_desc_get_irq_data(). static inline struct irq_data *irq_desc_get_irq_data(struct irq_desc *desc) { return &desc->irq_data; } > > Sashiko pointed out that irq_chip_retrigger_hierarchy() doesn't check > the outermost domain -- it immediately goes the parent. In v1 of this patch > series, you categorized this as a false positive. But I don’t understand > your explanation. Even if there aren't currently any outermost domains > with a custom retrigger function, there could be at some point in the > future. So it seems wrong to skip it. But maybe I'm missing something. > Could you elaborate on your reasoning? > > Michael > irq_chip_retrigger_hierarchy() deliberately skips the chip passed to it and begins with its parent, i.e. apic_retrigger_irq(). The new code was doing the same. However, if someone adds a custom .irq_retrigger, hoping that it would get executed, it would not. Sashiko's example was valid in principle, but it is not relevant to these device interrupts because desc->irq_data is the outer MSI/IOAPIC/Hyper-V chip. The LAPIC data is its parent, not the starting data. I found no device IRQ in this path whose descriptor starts directly at lapic_controller. I am all in for adding this as a fallback - + if (chip->irq_retrigger) + ret = chip->irq_retrigger(data); + else + ret = irq_chip_retrigger_hierarchy(data); This should solve this problem while still covering the chips which can forget to add a retrigger function. Please let me know if this looks good to you. >> __this_cpu_write(vector_irq[vector], VECTOR_RETRIGGERED); >> - } >> - raw_spin_unlock(&desc->lock); >> } >> + >> if (__this_cpu_read(vector_irq[vector]) != VECTOR_RETRIGGERED) >> __this_cpu_write(vector_irq[vector], VECTOR_UNUSED); >> } >> -- >> 2.43.0 >> > Regards, Naman