[Xen-devel] [PATCH 1/2] xen/sched: fix locking in restore_vcpu_affinity()

[Juergen Gross <jgross@xxxxxxxx>]

Commit 0763cd2687897b55e7 ("xen/sched: don't disable scheduler on cpus
during suspend") removed a lock in restore_vcpu_affinity() which needs
to stay: cpumask_scratch_cpu() must be protected by the scheduler
lock. restore_vcpu_affinity() is being called by thaw_domains(), so
with multiple domains in the system another domain might already be
running and the scheduler might make use of cpumask_scratch_cpu()
already.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 xen/common/schedule.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 25f6ab388d..89bc259ae4 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -708,6 +708,8 @@ void restore_vcpu_affinity(struct domain *d)
          * set v->processor of each of their vCPUs to something that will
          * make sense for the scheduler of the cpupool in which they are in.
          */
+        lock = vcpu_schedule_lock_irq(v);
+
         cpumask_and(cpumask_scratch_cpu(cpu), v->cpu_hard_affinity,
                     cpupool_domain_cpumask(d));
         if ( cpumask_empty(cpumask_scratch_cpu(cpu)) )
@@ -731,6 +733,9 @@ void restore_vcpu_affinity(struct domain *d)
 
         v->processor = cpumask_any(cpumask_scratch_cpu(cpu));
 
+        spin_unlock_irq(lock);
+
+       /* v->processor might have changed, so reacquire the lock. */
         lock = vcpu_schedule_lock_irq(v);
         v->processor = sched_pick_cpu(vcpu_scheduler(v), v);
         spin_unlock_irq(lock);
-- 
2.16.4


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