[PATCH] perf: arm_pmu_acpi: Fix armpmu_alloc call from invalid context

[Mark Salter <msalter@redhat.com>]

When booting an arm64 debug kernel with ACPI, I see:

   BUG: sleeping function called from invalid context at mm/slab.h:420
   in_atomic(): 0, irqs_disabled(): 128, pid: 12, name: cpuhp/0
   1 lock held by cpuhp/0/12:
    #0:  (cpuhp_state-up){+.+.}, at: [<0000000057aa0dae>] cpuhp_thread_fun+0x13c/0x258
   irq event stamp: 28
   hardirqs last  enabled at (27): [<000000000b861658>] _raw_spin_unlock_irq+0x38/0x58
   hardirqs last disabled at (28): [<000000006231cfb1>] cpuhp_thread_fun+0xd0/0x258
   softirqs last  enabled at (0): [<0000000054d9737a>] copy_process.isra.32.part.33+0x450/0x1480
   softirqs last disabled at (0): [<          (null)>]           (null)
   CPU: 0 PID: 12 Comm: cpuhp/0 Not tainted 4.15.0+ #18
   Hardware name: AppliedMicro X-Gene Mustang Board/X-Gene Mustang Board, BIOS 3.06.25 Oct 17 2016
   Call trace:
    dump_backtrace+0x0/0x188
    show_stack+0x24/0x2c
    dump_stack+0xa4/0xe0
    ___might_sleep+0x208/0x234
    __might_sleep+0x58/0x8c
    kmem_cache_alloc_trace+0x248/0x3e0
    armpmu_alloc+0x38/0x1a8
    arm_pmu_acpi_cpu_starting+0x11c/0x15c
    cpuhp_invoke_callback+0x120/0x100c
    cpuhp_thread_fun+0xe8/0x258
    smpboot_thread_fn+0x170/0x268
    kthread+0x110/0x13c
    ret_from_fork+0x10/0x18

With commit 7d88eb695a1f ("arm/perf: Convert to hotplug state machine"),
arm_pmu uses the cpuhotplug framework to initialize the PMU driver when
using ACPI. However, the arm_pmu_acpi_cpu_starting() callback comes
before CPUHP_AP_ONLINE is reached which means it runs with interrupts
diabled and tries to allocate memory with GFP_KERNEL alloc which may
sleep.

Move CPUHP_AP_PERF_ARM_ACPI_STARTING to come after CPUHP_AP_ONLINE so
that the arm_pmu initialization runs with interrupts enabled as it
does when booting with device tree.

Fixes: 7d88eb695a1f ("arm/perf: Convert to hotplug state machine")
Signed-off-by: Mark Salter <msalter@redhat.com>
---
 include/linux/cpuhotplug.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 5172ad0..e07b2da 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -114,7 +114,6 @@ enum cpuhp_state {
 	CPUHP_AP_ARM_VFP_STARTING,
 	CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
 	CPUHP_AP_PERF_ARM_HW_BREAKPOINT_STARTING,
-	CPUHP_AP_PERF_ARM_ACPI_STARTING,
 	CPUHP_AP_PERF_ARM_STARTING,
 	CPUHP_AP_ARM_L2X0_STARTING,
 	CPUHP_AP_ARM_ARCH_TIMER_STARTING,
@@ -146,6 +145,7 @@ enum cpuhp_state {
 	CPUHP_AP_SMPBOOT_THREADS,
 	CPUHP_AP_X86_VDSO_VMA_ONLINE,
 	CPUHP_AP_IRQ_AFFINITY_ONLINE,
+	CPUHP_AP_PERF_ARM_ACPI_STARTING,
 	CPUHP_AP_PERF_ONLINE,
 	CPUHP_AP_PERF_X86_ONLINE,
 	CPUHP_AP_PERF_X86_UNCORE_ONLINE,
-- 
1.8.3.1