[Xen-devel] [PATCH v2 2/2] xen: credit2: fix potential issues in csched2_cpu_pick with tracing enabled

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

In fact, when not finding a suitable runqueue where to
place a vCPU, and hence using a fallback, we either:
 - don't issue any trace record (while we should),
 - risk underruning when accessing the runqueues
   array, while preparing the trace record.

Fix both issues and, while there, also a couple of style
problems found nearby.

Spotted by Coverity.

Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
Cc: George Dunlap <george.dunlap@xxxxxxxxxx>
Cc: Anshul Makkar <anshul.makkar@xxxxxxxxxx>
---
Changes from v1:
 * cite Coverity in the changelog.
---
 xen/common/sched_credit2.c |   13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index a55240f..3009ff9 100644
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -1443,7 +1443,8 @@ csched2_cpu_pick(const struct scheduler *ops, struct vcpu 
*vc)
     {
         /* We may be here because someone requested us to migrate. */
         __clear_bit(__CSFLAG_runq_migrate_request, &svc->flags);
-        return get_fallback_cpu(svc);
+        new_cpu = get_fallback_cpu(svc);
+        goto out;
     }
 
     /* First check to see if we're here because someone else suggested a place
@@ -1505,7 +1506,7 @@ csched2_cpu_pick(const struct scheduler *ops, struct vcpu 
*vc)
         if ( rqd_avgload < min_avgload )
         {
             min_avgload = rqd_avgload;
-            min_rqi=i;
+            min_rqi = i;
         }
     }
 
@@ -1520,20 +1521,20 @@ csched2_cpu_pick(const struct scheduler *ops, struct 
vcpu *vc)
         BUG_ON(new_cpu >= nr_cpu_ids);
     }
 
-out_up:
+ out_up:
     read_unlock(&prv->lock);
-
+ out:
     if ( unlikely(tb_init_done) )
     {
         struct {
             uint64_t b_avgload;
             unsigned vcpu:16, dom:16;
             unsigned rq_id:16, new_cpu:16;
-       } d;
-        d.b_avgload = prv->rqd[min_rqi].b_avgload;
+        } d;
         d.dom = vc->domain->domain_id;
         d.vcpu = vc->vcpu_id;
         d.rq_id = c2r(ops, new_cpu);
+        d.b_avgload = prv->rqd[d.rq_id].b_avgload;
         d.new_cpu = new_cpu;
         __trace_var(TRC_CSCHED2_PICKED_CPU, 1,
                     sizeof(d),


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