Merge tag 'sched-urgent-2026-08-22' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fixes from Ingo Molnar:

 - Add missing cpus_read_lock locking to rebuild_sched_domains()
   (Sebastian Andrzej Siewior)

 - Fix division by zero bug in tg_cpus() that can be triggered with
   empty cpusets (Jake Steinman)

* tag 'sched-urgent-2026-08-22' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/fair: Floor tg_cpus() at 1
  sched/topology: Add a cpus_read_lock to rebuild_sched_domains()

Author: torvalds

include/linux/cpuset.h

@@ -279,6 +279,7 @@ static inline void dl_rebuild_rd_accounting(void)
 
 static inline void rebuild_sched_domains(void)
 {
+	guard(cpus_read_lock)();
 	partition_sched_domains(1, NULL, NULL);
 }
 

kernel/sched/fair.c

@@ -4934,7 +4934,12 @@ static int tg_cpus(struct task_group *tg)
 			nr = cpuset_num_cpus(cgrp);
 	}
 
-	return nr;
+	/*
+	 * An empty cpuset would propagate a 0 shares_max into
+	 * __calc_smp_shares(), where clamp() yields hi when hi < lo and so
+	 * defeats the MIN_SHARES floor. Match tg_tasks(), which floors at 1.
+	 */
+	return max(nr, 1);
 }
 
 static inline int tg_tasks(struct task_group *tg)