Messages in this thread Patch in this message | | | Date | Tue, 23 Mar 2004 20:37:55 -0800 | From | William Lee Irwin III <> | Subject | Re: [PATCH] nodemask_t x86_64 changes [5/7] |
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At some point in the past, I wrote: >> Any idea where this bogon might be?
On Tue, Mar 23, 2004 at 08:11:01PM -0800, Paul Jackson wrote: > Unless I'm missing something (quite possible), the following would > expose the complement operators setting of high unused bits. > You have 32 bit unsigned longs and NR_CPUS == 24, you complement > some cpumask, and you then ask if it is empty, or ask if it is > equal to another cpumask that differs only in the unused > high byte, or ask its Hamming weight? > The arithmetic cpumask ops don't mask off the unused bits above NR_CPUS. > This might never be noticed, because cpumask_complement is the only op > that sets these unused bits, the complement op is very rarely used, and > none of its current uses can lead to the above bugs that I see offhand.
It's supposed to do this. bitmap_weight() masks off the trailing bits to filter out "don't cares" from whole-word ops. Everything else operates bitwise. Something like the following will keep the bits clear as you wish, since apparently the more simplistic single-word ops aren't obeying this. It's likely possible to better this by exploiting some invariants; feel free improve on it.
-- wli
Index: pgcl-2.6.5-rc2/include/asm-generic/cpumask_arith.h =================================================================== --- pgcl-2.6.5-rc2.orig/include/asm-generic/cpumask_arith.h 2004-03-19 16:11:33.000000000 -0800 +++ pgcl-2.6.5-rc2/include/asm-generic/cpumask_arith.h 2004-03-23 20:34:54.000000000 -0800 @@ -6,6 +6,12 @@ * to contain the whole cpu bitmap. */ +#if NR_CPUS % BITS_PER_LONG +#define __CPU_MASK_VALID_BITS__ ((1UL << (NR_CPUS % BITS_PER_LONG)) - 1) +#else +#define __CPU_MASK_VALID_BITS__ (~0UL) +#endif + #define cpu_set(cpu, map) set_bit(cpu, &(map)) #define cpu_clear(cpu, map) clear_bit(cpu, &(map)) #define cpu_isset(cpu, map) test_bit(cpu, &(map)) @@ -14,15 +20,15 @@ #define cpus_and(dst,src1,src2) do { dst = (src1) & (src2); } while (0) #define cpus_or(dst,src1,src2) do { dst = (src1) | (src2); } while (0) #define cpus_clear(map) do { map = 0; } while (0) -#define cpus_complement(map) do { map = ~(map); } while (0) -#define cpus_equal(map1, map2) ((map1) == (map2)) -#define cpus_empty(map) ((map) == 0) +#define cpus_complement(map) do { map = ~(map) & __CPU_MASK_VALID_BITS__; } while (0) +#define cpus_equal(map1, map2) (!(((map1) ^ (map2)) & __CPU_MASK_VALID_BITS__)) +#define cpus_empty(map) (!((map) & __CPU_MASK_VALID_BITS__)) #define cpus_addr(map) (&(map)) #if BITS_PER_LONG == 32 -#define cpus_weight(map) hweight32(map) +#define cpus_weight(map) hweight32((map) & __CPU_MASK_VALID_BITS__) #elif BITS_PER_LONG == 64 -#define cpus_weight(map) hweight64(map) +#define cpus_weight(map) hweight64((map) & __CPU_MASK_VALID_BITS__) #endif #define cpus_shift_right(dst, src, n) do { dst = (src) >> (n); } while (0) @@ -39,11 +45,13 @@ #define CPU_MASK_NONE ((cpumask_t)0) /* only ever use this for things that are _never_ used on large boxen */ -#define cpus_coerce(map) ((unsigned long)(map)) +#define cpus_coerce(map) ((unsigned long)(map) & __CPU_MASK_VALID_BITS__) #define cpus_promote(map) ({ map; }) #define cpumask_of_cpu(cpu) ({ ((cpumask_t)1) << (cpu); }) #define first_cpu(map) __ffs(map) #define next_cpu(cpu, map) find_next_bit(&(map), NR_CPUS, cpu + 1) +#undef __CPU_MASK_VALID_BITS__ + #endif /* __ASM_GENERIC_CPUMASK_ARITH_H */ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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