[PATCH RFC 0/2] x86/apic: Avoid cm->allocated going negative in irq_matrix

[Vitaly Kuznetsov]

I discovered that CPU0 offlining/onlining works only once:

     # echo 0 > /sys/devices/system/cpu/cpu0/online
     # echo 1 > /sys/devices/system/cpu/cpu0/online
     # echo 0 > /sys/devices/system/cpu/cpu0/online
     -bash: echo: write error: No space left on device
    
    with the following in dmesg:
    
     [ ... ] CPU 0 has 4294967295 vectors, 589 available. Cannot disable CPU

And the problem seems to be that irq_matrix_assign()/irq_matrix_free() calls
for PIC_CASCADE_IR are unbalanced, making cm->allocated go negative.

RFC as I didn't quite get why we're making an exception for PIC_CASCADE_IR in
the first place. Surely it is special, but for the sake of consistency we'd
better not treat it as such. Or maybe I just misunderstood everythin.

Vitaly Kuznetsov (2):
  x86/apic: Do not make an exception for PIC_CASCADE_IR when marking
    legacy irqs in irq_matrix
  genirq/matrix: WARN_ON_ONCE() when cm->allocated/m->total_allocated go
    negative

 arch/x86/kernel/apic/vector.c |  3 +--
 kernel/irq/matrix.c           | 11 +++++++++--
 2 files changed, 10 insertions(+), 4 deletions(-)

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2.29.2