sched/topology: Check SDF_SHARED_CHILD in highest_flag_domain()

Do not assume that all the children of a scheduling domain have a given
flag. Check whether it has the SDF_SHARED_CHILD meta flag.

Suggested-by: Ionela Voinescu <[e-mail]>
Signed-off-by: Ricardo Neri <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

kernel/sched/sched.h

···
 	for (__sd = rcu_dereference_check_sched_domain(cpu_rq(cpu)->sd); \
 			__sd; __sd = __sd->parent)
 
+/* A mask of all the SD flags that have the SDF_SHARED_CHILD metaflag */
+#define SD_FLAG(name, mflags) (name * !!((mflags) & SDF_SHARED_CHILD)) |
+static const unsigned int SD_SHARED_CHILD_MASK =
+#include <linux/sched/sd_flags.h>
+0;
+#undef SD_FLAG
+
 /**
  * highest_flag_domain - Return highest sched_domain containing flag.
  * @cpu:	The CPU whose highest level of sched domain is to
···
  * @flag:	The flag to check for the highest sched_domain
  *		for the given CPU.
  *
- * Returns the highest sched_domain of a CPU which contains the given flag.
+ * Returns the highest sched_domain of a CPU which contains @flag. If @flag has
+ * the SDF_SHARED_CHILD metaflag, all the children domains also have @flag.
  */
 static inline struct sched_domain *highest_flag_domain(int cpu, int flag)
 {
 	struct sched_domain *sd, *hsd = NULL;
 
 	for_each_domain(cpu, sd) {
-		if (!(sd->flags & flag))
+		if (sd->flags & flag) {
+			hsd = sd;
+			continue;
+		}
+
+		/*
+		 * Stop the search if @flag is known to be shared at lower
+		 * levels. It will not be found further up.
+		 */
+		if (flag & SD_SHARED_CHILD_MASK)
 			break;
-		hsd = sd;
 	}
 
 	return hsd;