linux-kernel - Re: [PATCH 16/16] percpu: make accessors check for percpu pointer in sparse

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Date:	Thu, 15 Oct 2009 18:08:28 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Christoph Lameter <cl@...ux-foundation.org>
CC:	linux-kernel@...r.kernel.org, rusty@...tcorp.com.au,
	mingo@...hat.com, tglx@...utronix.de, akpm@...ux-foundation.org,
	rostedt@...dmis.org, hpa@...or.com, cebbert@...hat.com,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [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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