Booting the latest kernel with DEBUG_ATOMIC_SLEEP=y on a GICv4.1 enabled
box, I get the following kernel splat:

[    0.053766] BUG: sleeping function called from invalid context at mm/slab.h:567
[    0.053767] in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 0, name: swapper/1
[    0.053769] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.8.0-rc3+ #23
[    0.053770] Call trace:
[    0.053774]  dump_backtrace+0x0/0x218
[    0.053775]  show_stack+0x2c/0x38
[    0.053777]  dump_stack+0xc4/0x10c
[    0.053779]  ___might_sleep+0xfc/0x140
[    0.053780]  __might_sleep+0x58/0x90
[    0.053782]  slab_pre_alloc_hook+0x7c/0x90
[    0.053783]  kmem_cache_alloc_trace+0x60/0x2f0
[    0.053785]  its_cpu_init+0x6f4/0xe40
[    0.053786]  gic_starting_cpu+0x24/0x38
[    0.053788]  cpuhp_invoke_callback+0xa0/0x710
[    0.053789]  notify_cpu_starting+0xcc/0xd8
[    0.053790]  secondary_start_kernel+0x148/0x200

 # ./scripts/faddr2line vmlinux its_cpu_init+0x6f4/0xe40
its_cpu_init+0x6f4/0xe40:
allocate_vpe_l1_table at drivers/irqchip/irq-gic-v3-its.c:2818
(inlined by) its_cpu_init_lpis at drivers/irqchip/irq-gic-v3-its.c:3138
(inlined by) its_cpu_init at drivers/irqchip/irq-gic-v3-its.c:5166

It turned out that we're allocating memory using GFP_KERNEL (may sleep)
within the CPU hotplug notifier, which is indeed an atomic context. Bad
thing may happen if we're playing on a system with more than a single
CommonLPIAff group. Avoid it by turning this into an atomic allocation.

Fixes: 5e516846 ("irqchip/gic-v4.1: VPE table (aka GICR_VPROPBASER) allocation")
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200630133746.816-1-yuzenghui@huawei.com