[Xen-devel] [PATCH 1/6] xen/sched: call cpu_disable_scheduler() via cpu notifier

[Juergen Gross <jgross@xxxxxxxx>]

cpu_disable_scheduler() is being called from __cpu_disable() today.
There is no need to call it on the cpu just being disabled, so use
the CPU_DEAD case of the cpu notifier chain.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 xen/arch/x86/smpboot.c |  3 ---
 xen/common/schedule.c  | 12 +++++-------
 2 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
index 7d1226d7bc..b7a0a4a419 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -1221,9 +1221,6 @@ void __cpu_disable(void)
     cpumask_clear_cpu(cpu, &cpu_online_map);
     fixup_irqs(&cpu_online_map, 1);
     fixup_eoi();
-
-    if ( cpu_disable_scheduler(cpu) )
-        BUG();
 }
 
 void __cpu_die(unsigned int cpu)
diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 60755a631e..665747f247 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -773,8 +773,9 @@ void restore_vcpu_affinity(struct domain *d)
 }
 
 /*
- * This function is used by cpu_hotplug code from stop_machine context
+ * This function is used by cpu_hotplug code via cpu notifier chain
  * and from cpupools to switch schedulers on a cpu.
+ * Caller must get domlist_read_lock.
  */
 int cpu_disable_scheduler(unsigned int cpu)
 {
@@ -789,12 +790,6 @@ int cpu_disable_scheduler(unsigned int cpu)
     if ( c == NULL )
         return ret;
 
-    /*
-     * We'd need the domain RCU lock, but:
-     *  - when we are called from cpupool code, it's acquired there already;
-     *  - when we are called for CPU teardown, we're in stop-machine context,
-     *    so that's not be a problem.
-     */
     for_each_domain_in_cpupool ( d, c )
     {
         for_each_vcpu ( d, v )
@@ -1738,6 +1733,9 @@ static int cpu_schedule_callback(
         rc = cpu_schedule_up(cpu);
         break;
     case CPU_DEAD:
+        rcu_read_lock(&domlist_read_lock);
+        cpu_disable_scheduler(cpu);
+        rcu_read_unlock(&domlist_read_lock);
         SCHED_OP(sched, deinit_pdata, sd->sched_priv, cpu);
         /* Fallthrough */
     case CPU_UP_CANCELED:
-- 
2.16.4


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