Rework locking for sched_adjust.

The main idea is to move (as much as possible) locking logic
from generic code to the various pluggable schedulers.

While at it, the following is also accomplished:
 - pausing all the non-current VCPUs of a domain while changing its
   scheduling parameters is not effective in avoiding races and it is
   prone to deadlock, so that is removed.
 - sedf needs a global lock for preventing races while adjusting
   domains' scheduling parameters (as it is for credit and credit2),
   so that is added.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Acked-by: George Dunlap <george.dunlap@eu.citrix.com>
Committed-by: Keir Fraser <keir@xen.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
index 4fa6140da5..c959a47d65 100644
--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -161,6 +161,7 @@ struct csched_dom {
  * System-wide private data
  */
 struct csched_private {
+    /* lock for the whole pluggable scheduler, nests inside cpupool_lock */
     spinlock_t lock;
     struct list_head active_sdom;
     uint32_t ncpus;
@@ -800,6 +801,10 @@ csched_dom_cntl(
     struct csched_private *prv = CSCHED_PRIV(ops);
     unsigned long flags;
 
+    /* Protect both get and put branches with the pluggable scheduler
+     * lock. Runq lock not needed anywhere in here. */
+    spin_lock_irqsave(&prv->lock, flags);
+
     if ( op->cmd == XEN_DOMCTL_SCHEDOP_getinfo )
     {
         op->u.credit.weight = sdom->weight;
@@ -809,8 +814,6 @@ csched_dom_cntl(
     {
         ASSERT(op->cmd == XEN_DOMCTL_SCHEDOP_putinfo);
 
-        spin_lock_irqsave(&prv->lock, flags);
-
         if ( op->u.credit.weight != 0 )
         {
             if ( !list_empty(&sdom->active_sdom_elem) )
@@ -824,9 +827,10 @@ csched_dom_cntl(
         if ( op->u.credit.cap != (uint16_t)~0U )
             sdom->cap = op->u.credit.cap;
 
-        spin_unlock_irqrestore(&prv->lock, flags);
     }
 
+    spin_unlock_irqrestore(&prv->lock, flags);
+
     return 0;
 }