[Xen-changelog] [xen stable-4.4] sched: fix locking for insert_vcpu() in credit1 and RTDS

[patchbot@xxxxxxx]

commit 52f7217a10ffb692ae0e320830c17dcfeb7f6810
Author:     Dario Faggioli <dario.faggioli@xxxxxxxxxx>
AuthorDate: Tue Dec 15 15:52:51 2015 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Dec 15 15:52:51 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/schedule.c     |    6 ++----
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
index 81f3510..f08075d 100644
--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -910,9 +910,15 @@ 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/schedule.c b/xen/common/schedule.c
index 79768c5..f2a7427 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -1418,7 +1418,6 @@ 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;
@@ -1439,7 +1438,7 @@ 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;
@@ -1448,9 +1447,8 @@ 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-4.4

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