[Xen-devel] CONFIG_SPARSE_IRQ breaks single VCPU domain 0 between xen/master and xen/next

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

With a single VCPU domain 0 (either due to hardware on dom0_max_vcpus=1)
and CONFIG_SPARSE_IRQ on xen/next I see:

        Kernel panic - not syncing: No available IRQ to bind to: increase 
nr_irqs! (currently 256, started from 256)
        
        Pid: 0, comm: swapper Not tainted 2.6.32-x86_64-xen0 #5
        Call Trace:
         [<ffffffff813ae4a5>] panic+0xa0/0x17f
         [<ffffffff8100fb5f>] ? xen_restore_fl_direct_end+0x0/0x1
         [<ffffffff8118990e>] ? kvasprintf+0x6e/0x90
         [<ffffffff811cd87a>] find_unbound_irq+0x8a/0xb0
         [<ffffffff811cd941>] bind_virq_to_irq+0xa1/0x190
         [<ffffffff813ae5eb>] ? printk+0x67/0x6c
         [<ffffffff8100f7b0>] ? xen_timer_interrupt+0x0/0x1a0
         [<ffffffff811cde6d>] bind_virq_to_irqhandler+0x2d/0x80
         [<ffffffff8100f6e9>] xen_setup_timer+0x59/0x120
         [<ffffffff815cc8e1>] xen_time_init+0xa0/0xcf
         [<ffffffff815cd530>] x86_late_time_init+0xa/0x11
         [<ffffffff815c8d65>] start_kernel+0x31e/0x442
         [<ffffffff815c82b9>] x86_64_start_reservations+0x99/0xb9
         [<ffffffff815cba63>] xen_start_kernel+0x6a4/0x76e

it appears that nr_irqs == get_nr_irqs_gsi() in this configuration.

Seems to impact 32(on64) and 64 bit kernels.

xen/master (2.6.31.6) appears fine. I glanced through the diff between
xen/master and xen/next and nothing leaps out. xen/next is missing
e459de959 "Find an unbound irq number in reverse order (high to low)."
but I don't see how that make a difference (and it doesn't).

Ian.


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