linux-kernel - Re: [PATCH v1 2/4] LoongArch: Handle percpu handler address in bt

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Message-ID: <6ec0962a-8ba1-1bb9-c07d-1c344adef7fa@loongson.cn>
Date: Tue, 20 Jan 2026 21:08:34 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/4] LoongArch: Handle percpu handler address in
 bt_address()

On 2026/1/20 下午9:01, Huacai Chen wrote:
> On Tue, Jan 20, 2026 at 8:57 PM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
>>
>> On 2026/1/20 下午8:04, Huacai Chen wrote:
>>> Hi, Tiezhu,
>>>
>>> On Tue, Jan 20, 2026 at 5:23 PM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
>>>>
>>>> After commit 4cd641a79e69 ("LoongArch: Remove unnecessary checks for
>>>> ORC unwinder"), the system can not boot normally under some configs,
>>>> there are many error messages "cannot find unwind pc at".
>>
>> ...
>>
>>>> +#if defined(CONFIG_NUMA) && !defined(CONFIG_PREEMPT_RT)
>>>> +       for (int cpu = 1; cpu < num_possible_cpus(); cpu++) {
>>> Use nr_cpu_ids instead of num_possible_cpus() can improve performance a little.
>>>
>>>> +               int vec_sz = sizeof(exception_handlers);
>>>> +
>>> It is better to add "if (!pcpu_handlers[cpu]) continue" here.
>>
>> If so, it can use for_each_possible_cpu(cpu) directly?
> It can, but I remember you want to skip CPU 0?

Yes, that is the intention to use the for loop, but if checking
!pcpu_handlers[cpu], I think no need to use for loop to skip cpu
0, just use for_each_possible_cpu(cpu) is more simple and direct.

The code looks like:

----->8-----
diff --git a/arch/loongarch/kernel/unwind_orc.c 
b/arch/loongarch/kernel/unwind_orc.c
index d6b3688a1ce9..a0ba4e416f99 100644
--- a/arch/loongarch/kernel/unwind_orc.c
+++ b/arch/loongarch/kernel/unwind_orc.c
@@ -352,6 +352,24 @@ static inline unsigned long bt_address(unsigned 
long ra)
  {
         extern unsigned long eentry;

+#if defined(CONFIG_NUMA) && !defined(CONFIG_PREEMPT_RT)
+       int cpu;
+       int vec_sz __maybe_unused;
+
+       for_each_possible_cpu(cpu) {
+               if (!pcpu_handlers[cpu])
+                       continue;
+
+               vec_sz = sizeof(exception_handlers);
+
+               if (ra >= pcpu_handlers[cpu] &&
+                   ra < pcpu_handlers[cpu] + vec_sz) {
+                       ra = eentry + (ra - pcpu_handlers[cpu]);
+                       break;
+               }
+       }
+#endif
+
         if (ra >= eentry && ra < eentry +  EXCCODE_INT_END * VECSIZE) {
                 unsigned long func;
                 unsigned long type = (ra - eentry) / VECSIZE;

Please let me know what is the better way.

Thanks,
Tiezhu