[Xen-changelog] [xen stable-4.6] sched: fix locking for insert_vcpu() in credit1 and RTDS

[patchbot@xxxxxxx]

commit 880b5f3012893ded410a05522cc50ad94b02d890
Author:     Dario Faggioli <dario.faggioli@xxxxxxxxxx>
AuthorDate: Tue Dec 15 15:22:29 2015 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Dec 15 15:22:29 2015 +0100

    sched: fix locking for insert_vcpu() in credit1 and RTDS
    
    The insert_vcpu() hook is handled with inconsistent locking.
    In fact, schedule_cpu_switch() calls the hook with runqueue
    lock held, while sched_move_domain() relies on the hook
    implementations to take the lock themselves (and, since that
    is not done in Credit1 and RTDS, such operation is not safe
    in those cases).
    
    This is fixed as follows:
     - take the lock in the hook implementations, in specific
       schedulers' code;
     - avoid calling insert_vcpu(), for the idle vCPU, in
       schedule_cpu_switch(). In fact, idle vCPUs are set to run
       immediately, and the various schedulers won't insert them
       in their runqueues anyway, even when explicitly asked to.
    
    While there, still in schedule_cpu_switch(), locking with
    _irq() is enough (there's no need to do *_irqsave()).
    
    Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
    Reviewed-by: Meng Xu <mengxu@xxxxxxxxxxxxx>
    Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx>
    master commit: ae2f41e3d7e7798537b7ea6dbb9a0c6aeb1179e3
    master date: 2015-11-24 14:48:34 +0100
---
 xen/common/sched_credit.c |    6 ++++++
 xen/common/sched_rt.c     |    3 +++
 xen/common/schedule.c     |    6 ++----
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
index 57967c1..507e957 100644
--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -905,9 +905,15 @@ static void
 csched_vcpu_insert(const struct scheduler *ops, struct vcpu *vc)
 {
     struct csched_vcpu *svc = vc->sched_priv;
+    spinlock_t *lock;
+    unsigned long flags;
+
+    lock = vcpu_schedule_lock_irqsave(vc, &flags);
 
     if ( !__vcpu_on_runq(svc) && vcpu_runnable(vc) && !vc->is_running )
         __runq_insert(vc->processor, svc);
+
+    vcpu_schedule_unlock_irqrestore(lock, flags, vc);
 }
 
 static void
diff --git a/xen/common/sched_rt.c b/xen/common/sched_rt.c
index 4372486..da590ee 100644
--- a/xen/common/sched_rt.c
+++ b/xen/common/sched_rt.c
@@ -622,16 +622,19 @@ rt_vcpu_insert(const struct scheduler *ops, struct vcpu 
*vc)
 {
     struct rt_vcpu *svc = rt_vcpu(vc);
     s_time_t now = NOW();
+    spinlock_t *lock;
 
     /* not addlocate idle vcpu to dom vcpu list */
     if ( is_idle_vcpu(vc) )
         return;
 
+    lock = vcpu_schedule_lock_irq(vc);
     if ( now >= svc->cur_deadline )
         rt_update_deadline(now, svc);
 
     if ( !__vcpu_on_q(svc) && vcpu_runnable(vc) && !vc->is_running )
         __runq_insert(ops, svc);
+    vcpu_schedule_unlock_irq(lock, vc);
 
     /* add rt_vcpu svc to scheduler-specific vcpu list of the dom */
     list_add_tail(&svc->sdom_elem, &svc->sdom->vcpu);
diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 3eefed7..49bced4 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -1488,7 +1488,6 @@ void __init scheduler_init(void)
 
 int schedule_cpu_switch(unsigned int cpu, struct cpupool *c)
 {
-    unsigned long flags;
     struct vcpu *idle;
     spinlock_t *lock;
     void *ppriv, *ppriv_old, *vpriv, *vpriv_old;
@@ -1509,7 +1508,7 @@ int schedule_cpu_switch(unsigned int cpu, struct cpupool 
*c)
         return -ENOMEM;
     }
 
-    lock = pcpu_schedule_lock_irqsave(cpu, &flags);
+    lock = pcpu_schedule_lock_irq(cpu);
 
     SCHED_OP(old_ops, tick_suspend, cpu);
     vpriv_old = idle->sched_priv;
@@ -1518,9 +1517,8 @@ int schedule_cpu_switch(unsigned int cpu, struct cpupool 
*c)
     ppriv_old = per_cpu(schedule_data, cpu).sched_priv;
     per_cpu(schedule_data, cpu).sched_priv = ppriv;
     SCHED_OP(new_ops, tick_resume, cpu);
-    SCHED_OP(new_ops, insert_vcpu, idle);
 
-    pcpu_schedule_unlock_irqrestore(lock, flags, cpu);
+    pcpu_schedule_unlock_irq(lock, cpu);
 
     SCHED_OP(old_ops, free_vdata, vpriv_old);
     SCHED_OP(old_ops, free_pdata, ppriv_old, cpu);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.6

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