Re: [PATCH for-4.19 0/9] x86/irq: fixes for CPU hot{,un}plug

["Oleksii K." <oleksii.kurochko@xxxxxxxxx>]

On Wed, 2024-05-29 at 11:01 +0200, Roger Pau Monne wrote:
> Hello,
> 
> The following series aim to fix interrupt handling when doing CPU
> plug/unplug operations.  Without this series running:
> 
> cpus=`xl info max_cpu_id`
> while [ 1 ]; do
>     for i in `seq 1 $cpus`; do
>         xen-hptool cpu-offline $i;
>         xen-hptool cpu-online $i;
>     done
> done
> 
> Quite quickly results in interrupts getting lost and "No irq handler
> for
> vector" messages on the Xen console.  Drivers in dom0 also start
> getting
> interrupt timeouts and the system becomes unusable.
> 
> After applying the series running the loop over night still result in
> a
> fully usable system, no  "No irq handler for vector" messages at all,
> no
> interrupt loses reported by dom0.  Test with
> x2apic-mode={mixed,cluster}.
> 
> I'm tagging this for 4.19 as it's IMO bugfixes, but the series has
> grown
> quite bigger than expected, and hence we need to be careful to not
> introduce breakages late in the release cycle.  I've attempted to
> document all code as good as I could, interrupt handling has some
> unexpected corner cases that are hard to diagnose and reason about.
Despite of the fact that it can be considered as bugfixes, it seems to
me that this patch series can be risky. Let's wait for maintainers
opinion...

~ Oleksii
> 
> I'm currently also doing some extra testing with XenRT in case I've
> missed something.
> 
> Thanks, Roger.
> 
> Roger Pau Monne (9):
>   x86/irq: remove offline CPUs from old CPU mask when adjusting
>     move_cleanup_count
>   xen/cpu: do not get the CPU map in stop_machine_run()
>   xen/cpu: ensure get_cpu_maps() returns false if CPU operations are
>     underway
>   x86/irq: describe how the interrupt CPU movement works
>   x86/irq: limit interrupt movement done by fixup_irqs()
>   x86/irq: restrict CPU movement in set_desc_affinity()
>   x86/irq: deal with old_cpu_mask for interrupts in movement in
>     fixup_irqs()
>   x86/irq: handle moving interrupts in _assign_irq_vector()
>   x86/irq: forward pending interrupts to new destination in
> fixup_irqs()
> 
>  xen/arch/x86/apic.c             |   5 +
>  xen/arch/x86/include/asm/apic.h |   3 +
>  xen/arch/x86/include/asm/irq.h  |  28 +++++-
>  xen/arch/x86/irq.c              | 172 +++++++++++++++++++++++++-----
> --
>  xen/common/cpu.c                |   8 +-
>  xen/common/stop_machine.c       |  15 +--
>  xen/include/xen/cpu.h           |   2 +
>  xen/include/xen/rwlock.h        |   2 +
>  8 files changed, 190 insertions(+), 45 deletions(-)
>