[PATCH v2] arm64: perf: Fix access percpu variables in preemptible context

[Lecopzer Chen]

commit 367c820ef08082 ("arm64: Enable perf events based hard lockup detector")
reinitilizes lockup detector after arm64 PMU is initialized and open
a window for accessing smp_processor_id() in preemptible context.
Since hardlockup_detector_perf_init() always called in init stage
with a single cpu, but we initialize lockup detector after the init task
is migratable.

Fix this by utilizing lockup detector reconfiguration which calls
softlockup_start_all() on each cpu and calls watatchdog_nmi_enable() later.
Because softlockup_start_all() use IPI call function to make sure
watatchdog_nmi_enable() will bind on each cpu and fix this issue.

    BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1
    caller is debug_smp_processor_id+0x20/0x2c
    CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.10.0+ #276
    Hardware name: linux,dummy-virt (DT)
    Call trace:
      dump_backtrace+0x0/0x3c0
      show_stack+0x20/0x6c
      dump_stack+0x2f0/0x42c
      check_preemption_disabled+0x1cc/0x1dc
      debug_smp_processor_id+0x20/0x2c
      hardlockup_detector_event_create+0x34/0x18c
      hardlockup_detector_perf_init+0x2c/0x134
      watchdog_nmi_probe+0x18/0x24
      lockup_detector_init+0x44/0xa8
      armv8_pmu_driver_init+0x54/0x78
      do_one_initcall+0x184/0x43c
      kernel_init_freeable+0x368/0x380
      kernel_init+0x1c/0x1cc
      ret_from_fork+0x10/0x30


Fixes: 367c820ef08082 ("arm64: Enable perf events based hard lockup detector")
Signed-off-by: Lecopzer Chen <lecopzer.chen@xxxxxxxxxxxx>
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Cc: Sumit Garg <sumit.garg@xxxxxxxxxx>
---

Changelog v1 -> v2:
* https://lore.kernel.org/lkml/20201217130617.32202-1-lecopzer.chen@xxxxxxxxxxxx/
* Move solution from kernel/watchdog_hld.c to arm64 perf_event
    * avoid preemptive kmalloc in preempt_disable().



 arch/arm64/kernel/perf_event.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 38bb07eff872..c03e21210bbb 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -1345,4 +1345,20 @@ u64 hw_nmi_get_sample_period(int watchdog_thresh)
 
 	return (u64)max_cpu_freq * watchdog_thresh;
 }
+
+/*
+ * hardlockup_detector_perf_init() always call in init stage with a single
+ * cpu. In arm64 case, we re-initialize lockup detector after pmu driver
+ * initialized. Lockup detector initial function use lots of percpu variables
+ * and this makes CONFIG_DEBUG_PREEMPT unhappy because we are now in
+ * preemptive context.
+ * Return 0 if the nmi is ready and register nmi hardlockup detector by
+ * lockup detector reconfiguration.
+ */
+int __init watchdog_nmi_probe(void)
+{
+	if (arm_pmu_irq_is_nmi())
+		return 0;
+	return -ENODEV;
+}
 #endif
-- 
2.25.1