Messages in this thread | | | Date | Tue, 26 Jan 2010 03:10:42 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 7/8] percpu: add __percpu sparse annotations to hw_breakpoint |
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On Tue, Jan 26, 2010 at 03:01:14AM +0100, Frederic Weisbecker wrote: > On Tue, Jan 26, 2010 at 10:19:04AM +0900, Tejun Heo wrote: > > Hello, > > > > On 01/26/2010 10:02 AM, Frederic Weisbecker wrote: > > > Well, sorry I must be missing something obvious, but is it impossible > > > to make per_cpu(var, cpu) returning something cast in: > > > > > > (typeof(var) __force) > > > > > > Or I guess you did that already and it is not working with static > > > arrays, or? > > > > Yeap, the definition looks like > > > > #define SHIFT_PERCPU_PTR(__p, __offset) ({ \ > > __verify_pcpu_ptr((__p)); \ > > RELOC_HIDE((typeof(*(__p)) __kernel __force *)(__p), (__offset)); \ > > }) > > > > #define per_cpu(var, cpu) \ > > (*SHIFT_PERCPU_PTR(&(var), per_cpu_offset(cpu))) > > > > but it just ends up putting the __force at the wrong layer. It seems > > that (typeof(var) __kernel __force) tell sparse var is in the kernel > > address space but not its members. > > > So, may be it considers you are applying the address space overriding > to the pointer to the type and not to the type itself. > > Consider: > > int __percpu i; > > What you do above *might* be considered as if SHIFT_PERCPU_PTR > returns something of a type: > > int * __percpu i; > > So the pointer is in the normal address space, but its content is in > __percpu address space. > > What if you do this: > > > #define SHIFT_PERCPU_PTR(__p, __offset) ({ \ > __verify_pcpu_ptr((__p)); \ > RELOC_HIDE((__p), (__offset)); \ > }) > > #define per_cpu(var, cpu) \ > (typeof(var) __kernel __force)(*SHIFT_PERCPU_PTR(&(var), per_cpu_offset(cpu))) > > This should work because &(var) should be dereferencable directly, since > it is not of type "__force t" but of type "*__force t" > > And you're not doing anymore this: > > *(int * __kernel __force) i; > but > *(int __kernel __force *) i;
The above is perhaps a bit confusing. To be more clear, in the first case you only cast the pointer to the type, which gives you a pointer valid in kernel space to data valid in percpu space.
The second case gives you something valid in kernel space for both.
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