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

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 31/12/2011 02:55, "Liu.yi" <liu.yi24@xxxxxxxxxx> wrote:

> 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:

Cc'ing George Dunlap. This is probably a good bug fix.

 -- Keir

> --- 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
> 
> 
> --
> View this message in context:
> http://xen.1045712.n5.nabble.com/credit-scheduler-svc-flags-access-race-tp5111
> 504p5111504.html
> Sent from the Xen - Dev mailing list archive at Nabble.com.
> 
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> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel



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