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SubjectRe: [PATCH 7/8] cpumask: Provide a generic set of CPUMASK_ALLOC macros
Bert Wesarg wrote:
> On Tue, Jul 15, 2008 at 23:14, Mike Travis <travis@sgi.com> wrote:
>> * Provide a generic set of CPUMASK_ALLOC macros patterned after the
>> SCHED_CPUMASK_ALLOC macros. This is used where multiple cpumask_t
>> variables are declared on the stack to reduce the amount of stack
>> space required.
>>
>> Based on linux-2.6.tip/master at the following commit:
>>
>> commit 0a91813e16ebd5c2d9b5c2acd5b7c91742112c4f
>> Merge: 9a635fa... 724dce0...
>> Author: Ingo Molnar <mingo@elte.hu>
>> Date: Tue Jul 15 14:55:17 2008 +0200
>>
>> Signed-off-by: Mike Travis <travis@sgi.com>
>> Cc: Paul Jackson <pj@sgi.com>
>> ---
>> include/linux/cpumask.h | 21 +++++++++++++++++++++
>> 1 file changed, 21 insertions(+)
>>
>> --- linux-2.6.tip.orig/include/linux/cpumask.h
>> +++ linux-2.6.tip/include/linux/cpumask.h
>> @@ -75,6 +75,17 @@
>> * CPU_MASK_NONE Initializer - no bits set
>> * unsigned long *cpus_addr(mask) Array of unsigned long's in mask
>> *
>> + *if NR_CPUS > BITS_PER_LONG
>> + * CPUMASK_ALLOC(m) Declares and allocates struct m *m =
>> + * (struct m *)kmalloc(sizeof(*m), ...)
> Shouldn't you mention the GFP_KERNEL flag? And the cast should not
> necessarily be mentioned in a comment.

Hmm, yes. I encountered the checkpatch warning about casting kmalloc and
changed the macro but not the comment. (And now there's room for adding
GFP_KERNEL to the comment! ;-)
>
>> + * CPUMASK_FREE(m) Macro for kfree(v)
> kfree(m)
>
>> + *else
>> + * CPUMASK_ALLOC(m) Declares struct m _m, *m = &_m
>> + * CPUMASK_FREE(m) Nop
>> + *endif
>> + * CPUMASK_VAR(v, m) Declares cpumask_t *v =
>> + * m + offset(struct m, v)
> offsetof
> and why can't you use a &(m->v)?

I thought about this but what if kmalloc fails? It's ok to add the
offset to a NULL pointer, but dereferencing a null pointer (even though
it's just to get the address) may introduce a fault, yes?

I'll look into this further. There was one other remnant from the
copy/paste that needed to be fixed:

-#define CPUMASK_ALLOC(m) struct allmasks _m, *m = &_m
+#define CPUMASK_ALLOC(m) struct m _m, *m = &_m

Thanks!
Mike


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