On 10/13/2015 04:48 PM, Ingo Molnar wrote:
>
> * Andrey Ryabinin <aryabi...@virtuozzo.com> wrote:
>
>> get_wchan() is racy by design, it may access volatile stack
>> of running task, thus it may access redzone in a stack frame
>> and cause KASAN to warn about this.
>>
>> Use READ_ONCE_NOCHECK() to silence these warnings.
>>
>> Reported-by: Sasha Levin <sasha.le...@oracle.com>
>> Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com>
>> ---
>> arch/x86/kernel/process.c | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
>> index 39e585a..e28db18 100644
>> --- a/arch/x86/kernel/process.c
>> +++ b/arch/x86/kernel/process.c
>> @@ -550,14 +550,14 @@ unsigned long get_wchan(struct task_struct *p)
>> if (sp < bottom || sp > top)
>> return 0;
>>
>> - fp = READ_ONCE(*(unsigned long *)sp);
>> + fp = READ_ONCE_NOCHECK(*(unsigned long *)sp);
>> do {
>> if (fp < bottom || fp > top)
>> return 0;
>> - ip = READ_ONCE(*(unsigned long *)(fp + sizeof(unsigned long)));
>> + ip = READ_ONCE_NOCHECK(*(unsigned long *)(fp + sizeof(unsigned
>> long)));
>> if (!in_sched_functions(ip))
>> return ip;
>> - fp = READ_ONCE(*(unsigned long *)fp);
>> + fp = READ_ONCE_NOCHECK(*(unsigned long *)fp);
>> } while (count++ < 16 && p->state != TASK_RUNNING);
>> return 0;
>> }
>
> Hm, exactly how is the 'red zone' defined? Is this about the current task
> mostly,
> or when doing get_wchan() on other tasks?
We doing get_whcan() *only* on other tasks:
520: if (!p || p == current || p->state == TASK_RUNNING)
521: return 0;
Current wouldn't be a problem for KASAN.
> Thanks,
>
> Ingo
>
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