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

2020-12-19 Thread Lecopzer Chen 


Thanks a lot, I'll try to fix this in anthoer way(patch v2) to avoid
regreesion other than arm64

BRs,
Lecopzer


> Greeting,
> 
> FYI, we noticed the following commit (built with gcc-9):
> 
> commit: 6e37d53a67753bcb12a0b9102cac85d98f8a0453 ("[PATCH] 
> kernel/watchdog_hld.c: Fix access percpu in preemptible context")
> url: 
> https://github.com/0day-ci/linux/commits/Lecopzer-Chen/kernel-watchdog_hld-c-Fix-access-percpu-in-preemptible-context/20201217-211549
> base: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git 
> accefff5b547a9a1d959c7e76ad539bf2480e78b
> 
> in testcase: boot
> 
> on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 8G
> 
> caused below changes (please refer to attached dmesg/kmsg for entire 
> log/backtrace):
> 
> If you fix the issue, kindly add following tag
> Reported-by: kernel test robot 
>

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

2020-12-19 Thread Lecopzer Chen 
BRs,
Lecopzer


> Greeting,
> 
> FYI, we noticed the following commit (built with gcc-9):
> 
> commit: 6e37d53a67753bcb12a0b9102cac85d98f8a0453 ("[PATCH] 
> kernel/watchdog_hld.c: Fix access percpu in preemptible context")
> url: 
> https://github.com/0day-ci/linux/commits/Lecopzer-Chen/kernel-watchdog_hld-c-Fix-access-percpu-in-preemptible-context/20201217-211549
> base: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git 
> accefff5b547a9a1d959c7e76ad539bf2480e78b
> 
> in testcase: boot
> 
> on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 8G
> 
> caused below changes (please refer to attached dmesg/kmsg for entire 
> log/backtrace):
> 
> If you fix the issue, kindly add following tag
> Reported-by: kernel test robot 
>

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

2020-12-17 Thread 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 [] 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 
Cc: Sumit Garg 

---
 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