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SubjectRe: [PATCH 16/16] percpu: make accessors check for percpu pointer in sparse
Christoph Lameter wrote:
> On Wed, 14 Oct 2009, Tejun Heo wrote:
>
>> #ifndef SHIFT_PERCPU_PTR
>> /* Weird cast keeps both GCC and sparse happy. */
>> -#define SHIFT_PERCPU_PTR(__p, __offset) \
>> - RELOC_HIDE((typeof(*(__p)) __kernel __force *)(__p), (__offset))
>> +#define SHIFT_PERCPU_PTR(__p, __offset) ({ \
>> + __verify_pcpu_ptr((__p)); \
>> + RELOC_HIDE((typeof(*(__p)) __kernel __force *)(__p), (__offset)); \
>> +})
>
> If you have the verification in SHIFT_PER_CPU_PTR then why do you need it
> elsewhere?

Because this_cpu_*() macros might not calculate addresses using
SHIFT_PERCPU_PTR().

>> #define __pcpu_size_call_return(stem, variable) \
>> ({ typeof(variable) pscr_ret__; \
>> + __verify_pcpu_ptr(&(variable)); \
>> switch(sizeof(variable)) { \
>> case 1: pscr_ret__ = stem##1(variable);break; \
>> case 2: pscr_ret__ = stem##2(variable);break; \
>> @@ -250,6 +251,7 @@ extern void __bad_size_call_parameter(void);
>>
>> #define __pcpu_size_call(stem, variable, ...) \
>> do { \
>> + __verify_pcpu_ptr(&(variable)); \
>> switch(sizeof(variable)) { \
>> case 1: stem##1(variable, __VA_ARGS__);break; \
>> case 2: stem##2(variable, __VA_ARGS__);break; \
>
> Would it not be better to put the verification in the arch code? The
> percpu_to/from_op may have multiple callsites (at least they have now). If
> you put it in there then all other stuff is covered.

I don't know. The way these ops are defined, adding
__verify_pcpu_ptr() to size_call macros reliably cover all percpu
cases and I much prefer things like this being done in generic code
rather than requiring each arch to do it. It's just more reliable
this way.

Thanks.

--
tejun


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