Re: cpumask conversions, or not?
Rusty Russell wrote:
> On Tuesday 09 December 2008 21:26:36 Mike Travis wrote:
>> Rusty Russell wrote:
>>> Hi all,
>>>
>>> The new cpumask conversions are going well, but unfortunately Stephen
>>> uncovered a nasty bug via linux-next: the new cpumask operators only go to
>>> nr_cpumask_bits which can be less than NR_CPUS if NR_CPUS > BITS_PER_LONG.
>>> The undefined bits confuse the old cpumask operators. We fixed one case,
>>> but I am concerned that we will break archs as we convert more core code.
>> Hi Rusty,
>>
>> I think we can avoid this problem if we make cpumask_bits == NR_CPUS iff
>> CONFIG_CPUMASK_OFFSTACK=n. This complies with the current cpumask_t
>> approach and should cause all cpumask operators to always operate on
>> all cpumask bits.
>
> A very good point. And it's no worse than the old method.
>
> OK, forget about this for now, no urgent conversions needed :)
> Rusty.
This probably should be submitted through linux-next for wider test coverage?
Thanks,
Mike
---
cpumask: force nr_cpumask_bits to be NR_CPUS when CPUMASK_OFFSTACK is false
This maintains compatibility with the current cpumask_t. Once an architecture
is "cpumask clean" [IOW, all references span 0..(nr_cpus_ids-1) only, ignoring
any bits >= nr_cpu_ids], then it can set CPUMASK_OFFSTACK=y.
Signed-off-by: Mike Travis <travis@xxxxxxx>
---
include/linux/cpumask.h | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
--- linux-2.6-for-ingo.orig/include/linux/cpumask.h
+++ linux-2.6-for-ingo/include/linux/cpumask.h
@@ -510,9 +510,6 @@ extern cpumask_t cpu_active_map;
[BITS_TO_LONGS(NR_CPUS)-1] = CPU_MASK_LAST_WORD \
}
-/* This produces more efficient code. */
-#define nr_cpumask_bits NR_CPUS
-
#else /* NR_CPUS > BITS_PER_LONG */
#define CPU_BITS_ALL \
@@ -521,9 +518,20 @@ extern cpumask_t cpu_active_map;
[BITS_TO_LONGS(NR_CPUS)-1] = CPU_MASK_LAST_WORD \
}
-#define nr_cpumask_bits nr_cpu_ids
#endif /* NR_CPUS > BITS_PER_LONG */
+#ifndef CONFIG_CPUMASK_OFFSTACK
+
+/* This produces more efficient code. */
+#define nr_cpumask_bits NR_CPUS
+
+#else
+
+/* This allows for variabled-sized cpumask's */
+#define nr_cpumask_bits nr_cpu_ids
+
+#endif
+
/* verify cpu argument to cpumask_* operators */
static inline unsigned int cpumask_check(unsigned int cpu)
{
--
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