Re: [PATCH] mask ADT: bitmap and bitop tweaks [1/22]

[Paul Jackson <pj@sgi.com>]

> akpm, this is needed for mainline.

How urgent to you consider this fix (masking unused bits in the
arithmetic (single unsigned long word) cpumask implementation?

So far as I know, the only way to get high bits set with correct
invocations is by using cpus_complement(), which I don't see anyone
doing.

So I believe that this patch fixes latent bugs, not current bugs.

And it would be my preference (not surprisingly) to fix this in a way
that is consistent with my mask ADT proposal (avoid setting unused bits
on proper calls; don't filter on Boolean/scalar predicate evaluations):

+#if NR_CPUS % BITS_PER_LONG
+#define __CPU_VALID_MASK__		(~((1UL<< (NR_CPUS%BITS_PER_LONG) - 1))
+#else
+#define __CPU_VALID_MASK__		(~0UL)
+#endif

-#define cpus_complement(map)		do { map = ~(map); } while (0)
+#define cpus_complement(map)		\
+	do { map = ~(map) & __CPU_VALID_MASK__; } while (0)

_instead_ of changing the several other macros to follow the
bitmap convention (let the unused bits remain dont-care, until
resolving a Boolean or scalar predicate).

-- 
                          I won't rest till it's the best ...
                          Programmer, Linux Scalability
                          Paul Jackson <pj@sgi.com> 1.650.933.1373