[PATCH] kernel/watchdog_hld.c: Fix access percpu in preemptible context

[Lecopzer Chen]

commit 367c820ef08082 ("arm64: Enable perf events based hard lockup detector")
reinitilizes lockup detector after arm64 PMU is initialized and provide
another chance for access smp_processor_id() in preemptible context.
Since hardlockup_detector_event_create() use many percpu relative variable,
just try to fix this by get/put_cpu()

    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.c...@mediatek.com>
Cc: Sumit Garg <sumit.g...@linaro.org>

---
 kernel/watchdog_hld.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c
index 247bf0b1582c..c591a1ea8eb3 100644
--- a/kernel/watchdog_hld.c
+++ b/kernel/watchdog_hld.c
@@ -165,7 +165,7 @@ static void watchdog_overflow_callback(struct perf_event 
*event,
 
 static int hardlockup_detector_event_create(void)
 {
-       unsigned int cpu = smp_processor_id();
+       unsigned int cpu = get_cpu();
        struct perf_event_attr *wd_attr;
        struct perf_event *evt;
 
@@ -176,11 +176,13 @@ static int hardlockup_detector_event_create(void)
        evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,
                                               watchdog_overflow_callback, 
NULL);
        if (IS_ERR(evt)) {
+               put_cpu();
                pr_debug("Perf event create on CPU %d failed with %ld\n", cpu,
                         PTR_ERR(evt));
                return PTR_ERR(evt);
        }
        this_cpu_write(watchdog_ev, evt);
+       put_cpu();
        return 0;
 }
 
-- 
2.25.1