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From:   Thomas Gleixner <tglx@linutronix.de>
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To:     Bjorn Helgaas <helgaas@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, Wenwen Wang <wang6495@umn.edu>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 086/190] Revert "x86/PCI: Fix PCI IRQ routing table memory leak"
In-Reply-To: <20210422050919.GA2913711@bjorn-Precision-5520>
References: <20210422050919.GA2913711@bjorn-Precision-5520>
Date:   Fri, 23 Apr 2021 11:53:31 +0200
Message-ID: <87a6ppwcmc.ffs@nanos.tec.linutronix.de>
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On Thu, Apr 22 2021 at 00:09, Bjorn Helgaas wrote:
> On Wed, Apr 21, 2021 at 02:59:21PM +0200, Greg Kroah-Hartman wrote:
> I would prefer that you not apply this revert.
>
> Prior to ea094d53580f ("x86/PCI: Fix PCI IRQ routing table memory
> leak"), we had essentially this:
>
>   pcibios_irq_init()
>     pirq_table = pcibios_get_irq_routing_table();  # kmallocs
>     if (pirq_table) {
>       if (io_apic_assign_pci_irqs)
> 	pirq_table = NULL;
>     }
>
> So if we called pcibios_get_irq_routing_table(), we kmalloced some
> space and then (if io_apic_assign_pci_irqs) threw away the pointer,
> which leaks the pointer as the commit log says.
>
> After ea094d53580f, we have:
>
>   pcibios_irq_init()
>     rtable = NULL;
>     pirq_table = pcibios_get_irq_routing_table();  # kmallocs
>     rtable = pirq_table;
>     if (pirq_table) {
>       if (io_apic_assign_pci_irqs) {
>         kfree(rtable);
> 	pirq_table = NULL;
>       }
>     }
>
> which seems right to me.

It is correct.

Though looking at it again, the question is why this invokes
pcibios_get_irq_routing_table() at all if io_apic_assign_pci_irqs is
true?

Thanks,

        tglx