Re: [PATCH] x86/irq: Cure live lock in irq_force_complete_move()

From: Luck, Tony
Date: Fri Mar 11 2016 - 17:34:06 EST

With this patch applied my system survives me doing
several rounds of:

# echo 0 | tee /sys/devices/system/cpu/cpu*/online
# echo 1 | tee /sys/devices/system/cpu/cpu*/online

whereas without the patch the first of those went to

[152455.129604] NMI watchdog: Watchdog detected hard LOCKUP on cpu 96
[152455.136943] Kernel panic - not syncing: Hard LOCKUP

I'm not sure we care to optimize the cpu offline path, but I'll note here
that taking all (but one) cpus offline took 52 seconds (for a hundred
and mumble logical cpus). Bringing them all back is just 4 seconds.

Tested-by: Tony Luck <tony.luck@xxxxxxxxx>