linux-kernel - Re: [PATCH] x86/irq: Probe for PIC presence before allocating descs for legacy IRQs

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Date:	Mon, 2 Nov 2015 20:09:20 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
cc:	x86@...nel.org, Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/irq: Probe for PIC presence before allocating descs
 for legacy IRQs

Vitaly!

On Mon, 2 Nov 2015, Vitaly Kuznetsov wrote:
> Commit d32932d02e18 ("x86/irq: Convert IOAPIC to use hierarchical irqdomain
> interfaces") brought a regression for Hyper-V Gen2 instances. These
> instances don't have i8259 legacy PIC but they use legacy IRQs for serial
> port, rtc, and acpi. With this commit included we end up with these IRQs
> not initialized. Earlier, there was a special workaround for legacy IRQs
> in mp_map_pin_to_irq() doing mp_irqdomain_map() without looking at
> nr_legacy_irqs() and now we fail in __irq_domain_alloc_irqs() when
> irq_domain_alloc_descs() returns -EEXIST.
> 
> The essence of the issue seems to be that early_irq_init() calls
> arch_probe_nr_irqs() to figure out the number of legacy IRQs before
> we probe for i8259 and gets 16. Later when init_8259A() is called we switch
> to NULL legacy PIC and nr_legacy_irqs() starts to return 0 but we already
> have 16 descs allocated.
> 
> Solve the issue by separating i8259 probe from init and calling it in
> arch_probe_nr_irqs() before we actually use nr_legacy_irqs() information.

Nice catch!
 
> Fixes: d32932d02e18 ("x86/irq: Convert IOAPIC to use hierarchical irqdomain interfaces")
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/include/asm/i8259.h  |  1 +
>  arch/x86/kernel/apic/vector.c |  3 +++
>  arch/x86/kernel/i8259.c       | 24 ++++++++++++++++--------
>  3 files changed, 20 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/include/asm/i8259.h b/arch/x86/include/asm/i8259.h
> index ccffa53..bd55a77 100644
> --- a/arch/x86/include/asm/i8259.h
> +++ b/arch/x86/include/asm/i8259.h
> @@ -60,6 +60,7 @@ struct legacy_pic {
>  	void (*mask_all)(void);
>  	void (*restore_mask)(void);
>  	void (*init)(int auto_eoi);
> +	void (*probe)(void);
>  	int (*irq_pending)(unsigned int irq);
>  	void (*make_irq)(unsigned int irq);
>  };
> diff --git a/arch/x86/kernel/apic/vector.c b/arch/x86/kernel/apic/vector.c
> index 836d11b..aadd7ae 100644
> --- a/arch/x86/kernel/apic/vector.c
> +++ b/arch/x86/kernel/apic/vector.c
> @@ -361,6 +361,9 @@ int __init arch_probe_nr_irqs(void)
>  	if (nr < nr_irqs)
>  		nr_irqs = nr;
>  
> +	/* nr_legecy_irqs() depends on the PIC presence */
> +	legacy_pic->probe();
> +
>  	return nr_legacy_irqs();

We can simplify this by letting probe() return the number of legacy
interrupts, hmm?

Thanks,

	tglx
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