File 526f786a-fix-locking-in-cpu_disable_scheduler.p... of Package xen

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File 526f786a-fix-locking-in-cpu_disable_scheduler.patch of Package xen (Revision 24c36ffaeddb1eecf66fef5e4497553d)

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# Commit 41a0cc9e26160a89245c9ba3233e3f70bf9cd4b4
# Date 2013-10-29 09:57:14 +0100
# Author Jan Beulich <jbeulich@suse.com>
# Committer Jan Beulich <jbeulich@suse.com>
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@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Keir Fraser <keir@xen.org>

--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -600,7 +600,8 @@ int cpu_disable_scheduler(unsigned int c
     {
         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) &&
@@ -621,14 +622,12 @@ int cpu_disable_scheduler(unsigned int c
             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.
--- a/xen/common/stop_machine.c
+++ b/xen/common/stop_machine.c
@@ -110,6 +110,7 @@ int stop_machine_run(int (*fn)(void *), 
     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 *), 
     stopmachine_wait_state();
     ret = stopmachine_data.fn_result;
 
+    spin_debug_enable();
     stopmachine_set_state(STOPMACHINE_EXIT);
     stopmachine_wait_state();
     local_irq_enable();

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File 526f786a-fix-locking-in-cpu_disable_scheduler.patch of Package xen (Revision 24c36ffaeddb1eecf66fef5e4497553d)

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