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Commit 4200efd9 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

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: default avatarJeff Garzik <jeff@garzik.org>
Acked-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <alpine.LFD.2.01.0905180850110.3301@localhost.localdomain>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 2d02494f

include/linux/sched.h

+22 −3
Original line number Diff line number Diff line
@@ -839,7 +839,17 @@ struct sched_group { 
	 */

	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)
@@ -925,8 +935,17 @@ struct sched_domain { 
	char *name;

#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)

kernel/sched.c

+3 −2
Original line number Diff line number Diff line
@@ -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.

 * 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 sched_group sg;