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SubjectRe: [PATCH 1/4] Add support for userspace stacktraces in tracing/iter_ctrl
On 2008-10-12 16:31, Frédéric Weisbecker wrote:
> 2008/10/12 Török Edwin <edwintorok@gmail.com>:
>
>> +static int copy_stack_frame(const void __user *fp, struct stack_frame *frame)
>> +{
>> + int ret;
>> +
>> + if (!access_ok(VERIFY_READ, fp, sizeof(*frame)))
>> + return 0;
>> +
>> + ret = 1;
>> + pagefault_disable();
>> + if (__copy_from_user_inatomic(frame, fp, sizeof(*frame)))
>> + ret = 0;
>> + pagefault_enable();
>> +
>> + return ret;
>> +}
>> +
>>
>
> Hello Török,
>
> I don't understand why you are using this pagefault disabling and
> atomic copy here.
> Wouldn't a simple copy_from_user actually take of this? You don't seem
> to be in atomic
> context.
>

Hello,

This function is called from ftrace, as such I could be holding a
spinlock. It can also be called from
__rwsem_do_wake, which takes a spinlock.
This code is from sysprof's copy_stack_frame. Maybe pagefault_disable()
is not needed.

Best regards,
--Edwin
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