[RFC][PATCH] x86/hpet: fix NULL pointer dereference in msi_domain_alloc_irqs()

[Sergey Senozhatsky <sergey.senozhatsky@gmail.com>]

Fix the following oops:
 hpet_msi_get_hwirq+0x1f/0x27
 msi_domain_alloc+0x35/0xfe
 ? trace_hardirqs_on_caller+0x16c/0x188
 irq_domain_alloc_irqs_recursive+0x51/0x95
 __irq_domain_alloc_irqs+0x151/0x223
 hpet_assign_irq+0x5d/0x68
 hpet_msi_capability_lookup+0x121/0x1cb
 ? hpet_enable+0x2b4/0x2b4
 hpet_late_init+0x5f/0xf2
 ? hpet_enable+0x2b4/0x2b4
 do_one_initcall+0x184/0x199
 kernel_init_freeable+0x1af/0x237
 ? rest_init+0x13a/0x13a
 kernel_init+0xe/0xd4
 ret_from_fork+0x3f/0x70
 ? rest_init+0x13a/0x13a

since 3cb96f0c97330 (x86/hpet: Enhance HPET IRQ to support hierarchical
irqdomains') hpet_msi_capability_lookup() uses hpet_assign_irq(). the
latter discards `irq_alloc_info info' param and instead passes NULL to
__irq_domain_alloc_irqs() as `arg'. __irq_domain_alloc_irqs() invokes
irq_domain_alloc_irqs_recursive(), which msi_domain_alloc_irqs() and,
eventually, accesses `arg->hpet_index' in hpet_msi_get_hwirq().

directly call __irq_domain_alloc_irqs() in hpet_assign_irq() and pass
correct `arg' to fix the oops.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
 arch/x86/kernel/apic/msi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/apic/msi.c b/arch/x86/kernel/apic/msi.c
index 58fde66..440e0f9 100644
--- a/arch/x86/kernel/apic/msi.c
+++ b/arch/x86/kernel/apic/msi.c
@@ -351,6 +351,7 @@ int hpet_assign_irq(struct irq_domain *domain, struct hpet_dev *dev,
 	info.hpet_id = hpet_dev_id(domain);
 	info.hpet_index = dev_num;
 
-	return irq_domain_alloc_irqs(domain, 1, NUMA_NO_NODE, NULL);
+	return __irq_domain_alloc_irqs(domain, -1, 1, NUMA_NO_NODE,
+			&info, false);
 }
 #endif
-- 
2.4.0.53.g8440f74