[PATCH v2 sched_ext/for-7.3 26/36] sched_ext: Assign a unique id to each scheduler instance

[Tejun Heo <tj@kernel.org>]

Neither a scx_sched pointer nor its cgroup id uniquely identifies a
scheduler instance. A freed sched's memory can be reallocated, and a cgroup
can detach one sched and attach another. Add a monotonic, never-reused u64
id. A later patch compares it to drop a slice request that outlived a change
of a task's owning scheduler.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 kernel/sched/ext/ext.c      | 4 ++++
 kernel/sched/ext/internal.h | 3 +++
 2 files changed, 7 insertions(+)

diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index 796b857c7219..9fa4cfbc75c8 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -108,6 +108,9 @@ static bool dsq_is_rq_owned(struct scx_dispatch_q *dsq)
 	}
 }
 
+/* Cursor for unique scx_sched instance ids. id 0 is reserved. */
+static atomic64_t scx_sched_id_cursor = ATOMIC64_INIT(0);
+
 #ifdef CONFIG_EXT_SUB_SCHED
 /*
  * The sub sched being enabled. Used by scx_disable_and_exit_task() to exit
@@ -6442,6 +6445,7 @@ struct scx_sched *scx_alloc_and_add_sched(struct scx_enable_cmd *cmd,
 		       level * sizeof(parent->ancestors[0]));
 	sch->ancestors[level] = sch;
 	sch->level = level;
+	sch->id = atomic64_inc_return(&scx_sched_id_cursor);
 
 	if (ops->timeout_ms)
 		sch->watchdog_timeout = msecs_to_jiffies(ops->timeout_ms);
diff --git a/kernel/sched/ext/internal.h b/kernel/sched/ext/internal.h
index 5d4edd505ed1..0f3d98c19f7a 100644
--- a/kernel/sched/ext/internal.h
+++ b/kernel/sched/ext/internal.h
@@ -1444,6 +1444,9 @@ struct scx_sched {
 
 	struct list_head	all;
 
+	/* unique instance id, monotonic and never reused */
+	u64			id;
+
 #ifdef CONFIG_EXT_SUB_SCHED
 	struct rhash_head	hash_node;
 
-- 
2.54.0