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, 2 insertions, 32 deletions

diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 0455619ac2..3a91220823 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -1005,7 +1005,6 @@ int sched_id(void)
 /* Adjust scheduling parameter for a given domain. */
 long sched_adjust(struct domain *d, struct xen_domctl_scheduler_op *op)
 {
-    struct vcpu *v;
     long ret;
     
     if ( (op->sched_id != DOM2OP(d)->sched_id) ||
@@ -1013,40 +1012,11 @@ long sched_adjust(struct domain *d, struct xen_domctl_scheduler_op *op)
           (op->cmd != XEN_DOMCTL_SCHEDOP_getinfo)) )
         return -EINVAL;
 
-    /*
-     * Most VCPUs we can simply pause. If we are adjusting this VCPU then
-     * we acquire the local schedule_lock to guard against concurrent updates.
-     *
-     * We only acquire the local schedule lock after we have paused all other
-     * VCPUs in this domain. There are two reasons for this:
-     * 1- We don't want to hold up interrupts as pausing a VCPU can
-     *    trigger a tlb shootdown.
-     * 2- Pausing other VCPUs involves briefly locking the schedule
-     *    lock of the CPU they are running on. This CPU could be the
-     *    same as ours.
-     */
-
-    for_each_vcpu ( d, v )
-    {
-        if ( v != current )
-            vcpu_pause(v);
-    }
-
-    if ( d == current->domain )
-        vcpu_schedule_lock_irq(current);
-
+    /* NB: the pluggable scheduler code needs to take care
+     * of locking by itself. */
     if ( (ret = SCHED_OP(DOM2OP(d), adjust, d, op)) == 0 )
         TRACE_1D(TRC_SCHED_ADJDOM, d->domain_id);
 
-    if ( d == current->domain )
-        vcpu_schedule_unlock_irq(current);
-
-    for_each_vcpu ( d, v )
-    {
-        if ( v != current )
-            vcpu_unpause(v);
-    }
-
     return ret;
 }