[Xen-changelog] [xen stable-4.2] fix locking in cpu_disable_scheduler()

[patchbot@xxxxxxx]

commit bd1af50411b4a1afda5caf7e914e9554ce9166d7
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Nov 15 11:34:01 2013 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Nov 15 11:34:01 2013 +0100

    fix locking in cpu_disable_scheduler()
    
    So commit eedd6039 ("scheduler: adjust internal locking interface")
    uncovered - by now using proper spin lock constructs - a bug after all:
    When bringing down a CPU, cpu_disable_scheduler() gets called with
    interrupts disabled, and hence the use of vcpu_schedule_lock_irq() was
    never really correct (i.e. the caller ended up with interrupts enabled
    despite having disabled them explicitly).
    
    Fixing this however surfaced another problem: The call path
    vcpu_migrate() -> evtchn_move_pirqs() wants to acquire the event lock,
    which however is a non-IRQ-safe once, and hence check_lock() doesn't
    like this lock to be acquired when interrupts are already off. As we're
    in stop-machine context here, getting things wrong wrt interrupt state
    management during lock acquire/release is out of question though, so
    the simple solution to this appears to be to just suppress spin lock
    debugging for the period of time while the stop machine callback gets
    run.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Keir Fraser <keir@xxxxxxx>
    master commit: 41a0cc9e26160a89245c9ba3233e3f70bf9cd4b4
    master date: 2013-10-29 09:57:14 +0100
---
 xen/common/schedule.c     |    9 ++++-----
 xen/common/stop_machine.c |    2 ++
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 38661ea..3d516e6 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -586,7 +586,8 @@ int cpu_disable_scheduler(unsigned int cpu)
     {
         for_each_vcpu ( d, v )
         {
-            spinlock_t *lock = vcpu_schedule_lock_irq(v);
+            unsigned long flags;
+            spinlock_t *lock = vcpu_schedule_lock_irqsave(v, &flags);
 
             cpumask_and(&online_affinity, v->cpu_affinity, c->cpu_valid);
             if ( cpumask_empty(&online_affinity) &&
@@ -607,14 +608,12 @@ int cpu_disable_scheduler(unsigned int cpu)
             if ( v->processor == cpu )
             {
                 set_bit(_VPF_migrating, &v->pause_flags);
-                vcpu_schedule_unlock_irq(lock, v);
+                vcpu_schedule_unlock_irqrestore(lock, flags, v);
                 vcpu_sleep_nosync(v);
                 vcpu_migrate(v);
             }
             else
-            {
-                vcpu_schedule_unlock_irq(lock, v);
-            }
+                vcpu_schedule_unlock_irqrestore(lock, flags, v);
 
             /*
              * A vcpu active in the hypervisor will not be migratable.
diff --git a/xen/common/stop_machine.c b/xen/common/stop_machine.c
index 0590504..932e5a7 100644
--- a/xen/common/stop_machine.c
+++ b/xen/common/stop_machine.c
@@ -110,6 +110,7 @@ int stop_machine_run(int (*fn)(void *), void *data, 
unsigned int cpu)
     local_irq_disable();
     stopmachine_set_state(STOPMACHINE_DISABLE_IRQ);
     stopmachine_wait_state();
+    spin_debug_disable();
 
     stopmachine_set_state(STOPMACHINE_INVOKE);
     if ( (cpu == smp_processor_id()) || (cpu == NR_CPUS) )
@@ -117,6 +118,7 @@ int stop_machine_run(int (*fn)(void *), void *data, 
unsigned int cpu)
     stopmachine_wait_state();
     ret = stopmachine_data.fn_result;
 
+    spin_debug_enable();
     stopmachine_set_state(STOPMACHINE_EXIT);
     stopmachine_wait_state();
     local_irq_enable();
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.2

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