linux-kernel - Re: [PATCH v7 1/4] irqchip: gic: Support hierarchy irq domain.

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Message-ID: <87sihe9ncs.fsf@approximate.cambridge.arm.com>
Date:	Thu, 20 Nov 2014 10:29:23 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Yingjoe Chen <yingjoe.chen@...iatek.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Mark Rutland <Mark.Rutland@....com>,
	Boris BREZILLON <boris.brezillon@...e-electrons.com>,
	Russell King <linux@....linux.org.uk>,
	Jason Cooper <jason@...edaemon.net>,
	Pawel Moll <Pawel.Moll@....com>,
	"devicetree\@vger.kernel.org" <devicetree@...r.kernel.org>,
	"hc.yen\@mediatek.com" <hc.yen@...iatek.com>,
	"srv_heupstream\@mediatek.com" <srv_heupstream@...iatek.com>,
	"yh.chen\@mediatek.com" <yh.chen@...iatek.com>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"grant.likely\@linaro.org" <grant.likely@...aro.org>,
	Yijing Wang <wangyijing@...wei.com>,
	Rob Herring <robh+dt@...nel.org>,
	"nathan.chung\@mediatek.com" <nathan.chung@...iatek.com>,
	"yingjoe.chen\@gmail.com" <yingjoe.chen@...il.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	"eddie.huang\@mediatek.com" <eddie.huang@...iatek.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Sascha Hauer <kernel@...gutronix.de>,
	"linux- arm-kernel\@lists.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v7 1/4] irqchip: gic: Support hierarchy irq domain.

Hi Joe,

On Thu, Nov 20 2014 at  9:41:51 am GMT, Yingjoe Chen <yingjoe.chen@...iatek.com> wrote:
> Hi Marc,
>
> On Thu, 2014-11-20 at 11:57 +0800, Yingjoe Chen wrote:
>> On Wed, 2014-11-19 at 17:18 +0000, Marc Zyngier wrote:
>> > > +
>> > > +	return 0;
>> > > +}
>> > > +
>> > > +static const struct irq_domain_ops gic_irq_domain_hierarchy_ops = {
>> > > +	.xlate = gic_irq_domain_xlate,
>> > > +	.alloc = gic_irq_domain_alloc,
>> > > +	.free = irq_domain_free_irqs_top,
>> > 
>> > I'm convinced that irq_domain_free_irqs_top is the wrong function to
>> > call here, because you're calling it from the bottom, not the top-level
>> > (it has no parent).
>> 
>> Base on the name, I though this is helper function for top level
>> irq_domain?
>> 
>> > I cannot verify this with your code as I don't a working platform with
>> > GICv2m, but if I enable something similar on GICv3, it dies a very
>> > painful way:
>> > 
>> > Unable to handle kernel NULL pointer dereference at virtual address 00000018
>> > pgd = ffffffc03d059000
>> > [00000018] *pgd=0000000081356003, *pud=0000000081356003,
>> > *pmd=0000000000000000
>> > Internal error: Oops: 96000006 [#1] SMP
>> > Modules linked in:
>> > CPU: 4 PID: 1052 Comm: sh Not tainted 3.18.0-rc4+ #3311
>> > task: ffffffc03e320000 ti: ffffffc001390000 task.ti: ffffffc001390000
>> > PC is at irq_domain_free_irqs_recursive+0x1c/0x80
>> > LR is at irq_domain_free_irqs_common+0x88/0x9c
>> > pc : [<ffffffc0000ed790>] lr : [<ffffffc0000ede20>] pstate: 60000145
>> > [...]
>> > [<ffffffc0000ed790>] irq_domain_free_irqs_recursive+0x1c/0x80
>> > [<ffffffc0000ede1c>] irq_domain_free_irqs_common+0x84/0x9c
>> > [<ffffffc0000ede98>] irq_domain_free_irqs_top+0x64/0x7c <--
>> > gic_domain.free()
>> > [<ffffffc0000ed798>] irq_domain_free_irqs_recursive+0x24/0x80
>> > [<ffffffc0000ee468>] irq_domain_free_irqs_parent+0x14/0x20
>> > [<ffffffc0003500b8>] its_irq_domain_free+0xc8/0x250
>> > [<ffffffc0000ed798>] irq_domain_free_irqs_recursive+0x24/0x80
>> > [<ffffffc0000ede1c>] irq_domain_free_irqs_common+0x84/0x9c
>> > [<ffffffc0000ede98>] irq_domain_free_irqs_top+0x64/0x7c
>> > [<ffffffc0000ef518>] msi_domain_free+0x70/0x88
>> > [<ffffffc0000ed798>] irq_domain_free_irqs_recursive+0x24/0x80
>> > [<ffffffc0000ee3ac>] irq_domain_free_irqs+0x108/0x17c
>> > [<ffffffc0000efb68>] msi_domain_free_irqs+0x28/0x4c
>> > [<ffffffc000369cac>] free_msi_irqs+0xb4/0x1c0
>> > [<ffffffc00036adec>] pci_disable_msix+0x3c/0x4c
>> > [...]
>> > 
>> > and I cannot see how this could work on the standard GIC either.
>> 
>> I'm sorry, I just realize my testcase was too simple, irqs are populated
>> by device tree and never got freed. I'll add that and test it again.
>
> On a second thoughts, unlike the MSI cases, gic_irq_domain_hierarchy_ops
> is only used when we use DT, so we probably will never use the free
> function. Is it OK to remove the free support here?

Well, such thing is coming with GICv2m (SPIs are allocated out of
DT). You can drop it if you want, but I will then have to add it back
(which seems like a waste of time).

I'd prefer if you kept it in with the rest of the conversion.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny.
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