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sched: properly define the sched_group::cpumask and sched_domain::span fields 

Properly document the variable-size structure tricks we are doing
wrt. struct sched_group and sched_domain, and use the field[0] GCC
extension instead of defining a vla array.

Dont use unions for this, as pointed out by Linus.

[ Impact: cleanup, un-confuse Sparse and LLVM ]

Reported-by: Jeff Garzik <jeff@garzik.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <alpine.LFD.2.01.0905180850110.3301@localhost.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Ingo Molnar 2009-05-19 09:22:19 +02:00
parent 2d02494f5a
commit 4200efd9ac
2 changed files with 25 additions and 5 deletions
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25
include/linux/sched.h
View File

@ -839,7 +839,17 @@ struct sched_group {
*/ */
u32 reciprocal_cpu_power; u32 reciprocal_cpu_power;
unsigned long cpumask[]; /*
* The CPUs this group covers.
*
* NOTE: this field is variable length. (Allocated dynamically
* by attaching extra space to the end of the structure,
* depending on how many CPUs the kernel has booted up with)
*
* It is also be embedded into static data structures at build
* time. (See 'struct static_sched_group' in kernel/sched.c)
*/
unsigned long cpumask[0];
}; };
static inline struct cpumask *sched_group_cpus(struct sched_group *sg) static inline struct cpumask *sched_group_cpus(struct sched_group *sg)
@ -925,8 +935,17 @@ struct sched_domain {
char *name; char *name;
#endif #endif
/* span of all CPUs in this domain */ /*
unsigned long span[]; * Span of all CPUs in this domain.
*
* NOTE: this field is variable length. (Allocated dynamically
* by attaching extra space to the end of the structure,
* depending on how many CPUs the kernel has booted up with)
*
* It is also be embedded into static data structures at build
* time. (See 'struct static_sched_domain' in kernel/sched.c)
*/
unsigned long span[0];
}; };
static inline struct cpumask *sched_domain_span(struct sched_domain *sd) static inline struct cpumask *sched_domain_span(struct sched_domain *sd)

5
kernel/sched.c
View File

@ -7948,8 +7948,9 @@ int sched_smt_power_savings = 0, sched_mc_power_savings = 0;
/* /*
* The cpus mask in sched_group and sched_domain hangs off the end. * The cpus mask in sched_group and sched_domain hangs off the end.
* FIXME: use cpumask_var_t or dynamic percpu alloc to avoid wasting space *
* for nr_cpu_ids < CONFIG_NR_CPUS. * ( See the the comments in include/linux/sched.h:struct sched_group
* and struct sched_domain. )
*/ */
struct static_sched_group { struct static_sched_group {
struct sched_group sg; struct sched_group sg;