[Xen-devel] credit scheduler svc->flags access race?

["Liu.yi" <liu.yi24@xxxxxxxxxx>]

hi,all
In my HP DL380G7 server, csched_vcpu_yield and csched_acct may access
svc->flags at the same time, when this happens vms stop running because
csched_vcpu_yield overwrites svc->flags which csched_acct set to
CSCHED_FLAG_VCPU_PARKED (My vm's schedule cap values is not 0).
Vms run fine if I modified schedule_credit.c as follows:

--- xen/common/sched_credit.c   2010-12-10 10:19:45.000000000 +0800
+++ ../../xen-4.1.0/xen/common/sched_credit.c   2010-12-31
10:47:39.000000000 +0800
@@ -135,7 +135,7 @@ struct csched_vcpu {
     struct vcpu *vcpu;
     atomic_t credit;
     s_time_t start_time;   /* When we were scheduled (used for credit) */
-    uint16_t flags;
+    uint32_t flags;
     int16_t pri;
 #ifdef CSCHED_STATS
     struct {
@@ -787,7 +787,7 @@ csched_vcpu_yield(const struct scheduler
     if ( !sched_credit_default_yield )
     {
         /* Let the scheduler know that this vcpu is trying to yield */
-        sv->flags |= CSCHED_FLAG_VCPU_YIELD;
+        set_bit(1, &sv->flags);
     }
 }
 
@@ -1086,7 +1086,7 @@ csched_acct(void* dummy)
                 {
                     CSCHED_STAT_CRANK(vcpu_park);
                     vcpu_pause_nosync(svc->vcpu);
-                    svc->flags |= CSCHED_FLAG_VCPU_PARKED;
+                    set_bit(0, &svc->flags);
                 }
 
                 /* Lower bound on credits */
@@ -1111,7 +1111,7 @@ csched_acct(void* dummy)
                      */
                     CSCHED_STAT_CRANK(vcpu_unpark);
                     vcpu_unpause(svc->vcpu);
-                    svc->flags &= ~CSCHED_FLAG_VCPU_PARKED;
+                    clear_bit(0, &svc->flags);
                 }
 
                 /* Upper bound on credits means VCPU stops earning */
@@ -1337,7 +1337,7 @@ csched_schedule(
      * Clear YIELD flag before scheduling out
      */
     if ( scurr->flags & CSCHED_FLAG_VCPU_YIELD )
-        scurr->flags &= ~(CSCHED_FLAG_VCPU_YIELD);
+        clear_bit(1, &scurr->flags);

Are these modification correct? Another interesting thing is that vms run
fine on other server even if these vms's credit cap value is not 0. I don't
know why.
My xen version is 4.1.0, dom0 kernel version is 2.6.32.41 from jerry's git a
few months before.

Thanks

liuyi


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