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From: Thomas Gleixner <tglx@linutronix.de>
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To: Luigi Rizzo <lrizzo@google.com>, Marc Zyngier <maz@kernel.org>, Luigi
 Rizzo <rizzo.unipi@gmail.com>, Paolo Abeni <pabeni@redhat.com>, Andrew
 Morton <akpm@linux-foundation.org>, Sean Christopherson
 <seanjc@google.com>, Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Bjorn Helgaas
 <bhelgaas@google.com>, Willem de Bruijn <willemb@google.com>, Luigi Rizzo
 <lrizzo@google.com>
Subject: Re: [PATCH 2/6] genirq: soft_moderation: add base files, procfs hooks
In-Reply-To: <87346ie0vs.ffs@tglx>
References: <20251112192408.3646835-1-lrizzo@google.com>
 <20251112192408.3646835-3-lrizzo@google.com> <87346ie0vs.ffs@tglx>
Date: Thu, 13 Nov 2025 11:24:58 +0100
Message-ID: <87h5uycjr9.ffs@tglx>
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On Thu, Nov 13 2025 at 10:29, Thomas Gleixner wrote:
> On Wed, Nov 12 2025 at 19:24, Luigi Rizzo wrote:
>> +static void set_moderation_mode(struct irq_desc *desc, bool mode)
>> +{
>> +	if (desc) {
>
> Why would desc be NULL?
>
>> +		struct irq_chip *chip = desc->irq_data.chip;
>> +
>> +		/* Make sure this is msi and we can run enable_irq from irq context */
>> +		mode &= desc->handle_irq == handle_edge_irq && chip && chip->irq_bus_lock == NULL &&
>> +				chip->irq_bus_sync_unlock == NULL;

Q: How does this make sure that it is MSI?
A: Not at all

Q: How is this protected against concurrent modification?
A: Not at all

>> +		if (mode != desc->moderation_mode)
>> +			desc->moderation_mode = mode;

This conditional is truly making a difference.

Thanks

        tglx