Commit-ID: 4200efd9acda4accf24640f1e77d24fdcdb524df
Gitweb: http://git.kernel.org/tip/4200efd9acda4accf24640f1e77d24fdcdb524df
Author: Ingo Molnar <mingo@xxxxxxx>
AuthorDate: Tue, 19 May 2009 09:22:19 +0200
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Tue, 19 May 2009 09:22:19 +0200
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@xxxxxxxxxx>
Acked-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
LKML-Reference: <alpine.LFD.2.01.0905180850110.3301@xxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
include/linux/sched.h | 25 ++++++++++++++++++++++---
kernel/sched.c | 5 +++--
2 files changed, 25 insertions(+), 5 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index de7b3b2..dbb1043 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -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)
diff --git a/kernel/sched.c b/kernel/sched.c
index 497c09b..228acae 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -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;
--
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