Date:	Mon, 16 Nov 2015 16:00:37 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>, x86@...nel.org
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	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, xen-devel <xen-devel@...ts.xen.org>
Subject: Re: [PATCH v2] x86/irq: Probe for PIC presence before allocating
 descs for legacy IRQs

On 11/03/2015 04:40 AM, 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.
>
> Fixes: d32932d02e18 ("x86/irq: Convert IOAPIC to use hierarchical irqdomain interfaces")
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>

This breaks PV Xen with

[    0.000000] NR_IRQS:33024 nr_irqs:440 0

...

[    6.949434] BUG: unable to handle kernel NULL pointer dereference at           (null)
[    6.957564] IP: [<ffffffff8143d339>] xen_irq_init+0x29/0xe0
[    6.963385] PGD 0
[    6.965528] Oops: 0002 [#1] SMP
[    6.968927] Modules linked in:
[    6.972152] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.3.0upstream-12231-g3e546cd-dirty #1
[    6.980842] Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./To be filled by O.E.M., BIOS 080014  07/18/2008
[    6.992123] task: ffff880037992d00 ti: ffff880037994000 task.ti: ffff880037994000
[    6.999904] RIP: e030:[<ffffffff8143d339>]  [<ffffffff8143d339>] xen_irq_init+0x29/0xe0
[    7.008231] RSP: e02b:ffff880037997c48  EFLAGS: 00010246
[    7.013778] RAX: 0000000000000001 RBX: 0000000000000009 RCX: 0000000000000058
[    7.021204] RDX: 0000000000000000 RSI: 00000000024080c0 RDI: ffff880038000d88
[    7.028634] RBP: ffff880037997c58 R08: 0000000000000000 R09: ffff880037997be8
[    7.036062] R10: 0000000000000000 R11: ffff880038000df8 R12: 0000000000000009
[    7.043491] R13: 0000000000000001 R14: 0000000000000009 R15: ffffffff819dfa04
[    7.050922] FS:  0000000000000000(0000) GS:ffff88003de00000(0000) knlGS:0000000000000000
[    7.059343] CS:  e033 DS: 0000 ES: 0000 CR0: 000000008005003b
[    7.065330] CR2: 0000000000000000 CR3: 0000000001c0b000 CR4: 0000000000000660
[    7.072759] Stack:
[    7.074905]  0000000000000009 0000000000000009 ffff880037997cb8 ffffffff8143e5f1
[    7.082601]  00ff880037997c88 0000000000000000 ffffffff81832820 0000000000000009
[    7.090299]  ffff880037997da4 0000000000000009 0000000000000000 00000000ffffffff
[    7.097999] Call Trace:
[    7.100601]  [<ffffffff8143e5f1>] xen_bind_pirq_gsi_to_irq+0x81/0x210
[    7.107313]  [<ffffffff815df37c>] xen_register_pirq.clone.0+0x9c/0xf0
[    7.114026]  [<ffffffff815df431>] acpi_register_gsi_xen+0x61/0xd0
[    7.120378]  [<ffffffff8108bd39>] acpi_gsi_to_irq+0x69/0x80
[    7.126199]  [<ffffffff813f4f14>] ? acpi_ev_remove_all_sci_handlers+0xa5/0xa5
[    7.133626]  [<ffffffff813d7bd7>] acpi_os_install_interrupt_handler+0x47/0xc5
[    7.141053]  [<ffffffff813f260c>] ? acpi_ev_gpe_initialize+0x230/0x240
[    7.147861]  [<ffffffff813f5021>] acpi_ev_install_sci_handler+0x3f/0x6a
[    7.154752]  [<ffffffff813f0f27>] ? acpi_ev_initialize_events+0x138/0x151
[    7.161823]  [<ffffffff813f0d38>] acpi_ev_install_xrupt_handlers+0x54/0x10b
[    7.169074]  [<ffffffff81d53ef9>] acpi_enable_subsystem+0x22d/0x27f
[    7.175605]  [<ffffffff81d522e0>] ? acpi_early_init+0xeb/0xeb
[    7.181599]  [<ffffffff81d52355>] acpi_init+0x75/0x294
[    7.186974]  [<ffffffff81d50d91>] ? video_setup+0x85/0x85
[    7.192612]  [<ffffffff81d522e0>] ? acpi_early_init+0xeb/0xeb
[    7.198607]  [<ffffffff81002081>] do_one_initcall+0x81/0x1b0
[    7.204516]  [<ffffffff81d0fb3b>] kernel_init_freeable+0x171/0x20c
[    7.210958]  [<ffffffff81d0fbd6>] ? kernel_init_freeable+0x20c/0x20c
[    7.217583]  [<ffffffff817522f0>] ? rest_init+0x90/0x90
[    7.223046]  [<ffffffff817522f9>] kernel_init+0x9/0xe0
[    7.228416]  [<ffffffff8175f30f>] ret_from_fork+0x3f/0x70
[    7.234054]  [<ffffffff817522f0>] ? rest_init+0x90/0x90
[    7.239513] Code: 00 00 55 48 89 e5 41 54 53 89 fb e8 e2 65 cc ff 31 d2 48 85 c0 74 08 48 8b 50 10 48 83 c2 18 48 8b 05 ec 72 3d 00 be c0 80 40 02 <48> 89 02 48 8b 05 e5 72 3d 00 48 89 42 08 48 8b 05 e2 72 3d 00
[    7.259023] RIP  [<ffffffff8143d339>] xen_irq_init+0x29/0xe0
[    7.264932]  RSP <ffff880037997c48>
[    7.268598] CR2: 0000000000000000
[    7.272095] ---[ end trace 725f5e1483cadab0 ]---
[    7.276921] Kernel panic - not syncing: Fatal exception
(XEN) Domain 0 crashed: rebooting machine in 5 seconds.


Xen expects legacy interrupts to be there (pretty much for the same 
reason as Hyper-V does) and with this change arch_probe_nr_irqs() 
returns zero and no descriptors are allocated.

We can allocate those descriptors as needed in xen_irq_init() (if we 
know that IRQs are legacy), although that would look somewhat ugly and 
out of place.

-boris

-boris
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