[Xen-changelog] [xen staging] xen/sched: call cpu_disable_scheduler() via cpu notifier

[patchbot@xxxxxxx]

commit 9b28696502d400832c012c3b3fecfebee6c75648
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Tue Apr 2 18:19:05 2019 +0200
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Thu Apr 4 11:10:06 2019 +0100

    xen/sched: call cpu_disable_scheduler() via cpu notifier
    
    cpu_disable_scheduler() is being called from __cpu_disable() today.
    There is no need to execute it on the cpu just being disabled, so use
    the CPU_DEAD case of the cpu notifier chain. Moving the call out of
    stop_machine() context is fine, as we just need to hold the domain RCU
    lock and need the scheduler percpu data to be still allocated.
    
    Add another hook for CPU_DOWN_PREPARE to bail out early in case
    cpu_disable_scheduler() would fail. This will avoid crashes in rare
    cases for cpu hotplug or suspend.
    
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Acked-by: Julien Grall <julien.grall@xxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/arm/smpboot.c |  2 --
 xen/arch/x86/smpboot.c |  3 ---
 xen/common/schedule.c  | 36 +++++++++++++++++++++++++++++-------
 3 files changed, 29 insertions(+), 12 deletions(-)

diff --git a/xen/arch/arm/smpboot.c b/xen/arch/arm/smpboot.c
index 25cd44549c..f756444362 100644
--- a/xen/arch/arm/smpboot.c
+++ b/xen/arch/arm/smpboot.c
@@ -386,8 +386,6 @@ void __cpu_disable(void)
     /* It's now safe to remove this processor from the online map */
     cpumask_clear_cpu(cpu, &cpu_online_map);
 
-    if ( cpu_disable_scheduler(cpu) )
-        BUG();
     smp_mb();
 
     /* Return to caller; eventually the IPI mechanism will unwind and the 
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 76d60785e2..86bd10945d 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 )
@@ -893,6 +888,24 @@ int cpu_disable_scheduler(unsigned int cpu)
     return ret;
 }
 
+static int cpu_disable_scheduler_check(unsigned int cpu)
+{
+    struct domain *d;
+    struct vcpu *v;
+    struct cpupool *c;
+
+    c = per_cpu(cpupool, cpu);
+    if ( c == NULL )
+        return 0;
+
+    for_each_domain_in_cpupool ( d, c )
+        for_each_vcpu ( d, v )
+            if ( v->affinity_broken )
+                return -EADDRINUSE;
+
+    return 0;
+}
+
 /*
  * In general, this must be called with the scheduler lock held, because the
  * adjust_affinity hook may want to modify the vCPU state. However, when the
@@ -1734,7 +1747,16 @@ static int cpu_schedule_callback(
     case CPU_UP_PREPARE:
         rc = cpu_schedule_up(cpu);
         break;
+    case CPU_DOWN_PREPARE:
+        rcu_read_lock(&domlist_read_lock);
+        rc = cpu_disable_scheduler_check(cpu);
+        rcu_read_unlock(&domlist_read_lock);
+        break;
     case CPU_DEAD:
+        rcu_read_lock(&domlist_read_lock);
+        rc = cpu_disable_scheduler(cpu);
+        BUG_ON(rc);
+        rcu_read_unlock(&domlist_read_lock);
         SCHED_OP(sched, deinit_pdata, sd->sched_priv, cpu);
         /* Fallthrough */
     case CPU_UP_CANCELED:
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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