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Subject[Patch 4/5] sched: introduce a mutex and corresponding API to serialize access to doms_cur[] array
doms_cur[] array represents various scheduling domains which are mutually
exclusive. Currently cpusets code can modify this array (by calling
partition_sched_domains()) as a result of user modifying sched_load_balance
flag for various cpusets.

This patch introduces a mutex and corresponding API (only when
CONFIG_FAIR_GROUP_SCHED is defined) which allows a reader to safely read the
doms_cur[] array w/o worrying abt concurrent modifications to the array.

The fair group scheduler code (introduced in next patch of this series)
makes use of this mutex to walk thr' doms_cur[] array while rebalancing
shares of task groups across cpus.

Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>

---
kernel/sched.c | 19 +++++++++++++++++++
1 files changed, 19 insertions(+)
Index: current/kernel/sched.c
===================================================================
--- current.orig/kernel/sched.c
+++ current/kernel/sched.c
@@ -186,6 +186,9 @@ static struct cfs_rq *init_cfs_rq_p[NR_C
*/
static DEFINE_MUTEX(task_group_mutex);

+/* doms_cur_mutex serializes access to doms_cur[] array */
+static DEFINE_MUTEX(doms_cur_mutex);
+
/* Default task group.
* Every task in system belong to this group at bootup.
*/
@@ -236,11 +239,23 @@ static inline void unlock_task_group_lis
mutex_unlock(&task_group_mutex);
}

+static inline void lock_doms_cur(void)
+{
+ mutex_lock(&doms_cur_mutex);
+}
+
+static inline void unlock_doms_cur(void)
+{
+ mutex_unlock(&doms_cur_mutex);
+}
+
#else

static inline void set_task_cfs_rq(struct task_struct *p, unsigned int cpu) { }
static inline void lock_task_group_list(void) { }
static inline void unlock_task_group_list(void) { }
+static inline void lock_doms_cur(void) { }
+static inline void unlock_doms_cur(void) { }

#endif /* CONFIG_FAIR_GROUP_SCHED */

@@ -6547,6 +6562,8 @@ void partition_sched_domains(int ndoms_n
{
int i, j;

+ lock_doms_cur();
+
/* always unregister in case we don't destroy any domains */
unregister_sched_domain_sysctl();

@@ -6587,6 +6604,8 @@ match2:
ndoms_cur = ndoms_new;

register_sched_domain_sysctl();
+
+ unlock_doms_cur();
}

#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)

--
Regards,
vatsa
-
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