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From: Dario Faggioli <dario.faggioli@citrix.com>
To: xen-devel@lists.xenproject.org
Cc: Anshul Makkar <anshul.makkar@citrix.com>,
	George Dunlap <george.dunlap@citrix.com>,
	David Vrabel <david.vrabel@citrix.com>
Subject: [PATCH 06/19] xen: credit2: read NOW() with the proper runq lock held
Date: Sat, 18 Jun 2016 01:12:00 +0200	[thread overview]
Message-ID: <146620512051.29766.574756341169521466.stgit@Solace.fritz.box> (raw)
In-Reply-To: <146620492155.29766.10321123657058307698.stgit@Solace.fritz.box>

Yet another situation very similar to 779511f4bf5ae
("sched: avoid races on time values read from NOW()").

In fact, when more than one runqueue is involved, we need
to make sure that the following does not happen:
 1. take the lock of 1st runq
 2. now = NOW()
 3. take the lock of 2nd runq
 4. use now

as, if we have to wait at step 3, the value in now may
be stale when we get to use it at step 4.

While there, fix the style of a label.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
---
Cc: George Dunlap <george.dunlap@citrix.com>
Cc: Anshul Makkar <anshul.makkar@citrix.com>
Cc: David Vrabel <david.vrabel@citrix.com>
---
 xen/common/sched_credit2.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index 9e8e561..50f8dfd 100644
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -1361,7 +1361,7 @@ static void balance_load(const struct scheduler *ops, int cpu, s_time_t now)
 
     __update_runq_load(ops, st.lrqd, 0, now);
 
-retry:
+ retry:
     if ( !spin_trylock(&prv->lock) )
         return;
 
@@ -1377,7 +1377,8 @@ retry:
              || !spin_trylock(&st.orqd->lock) )
             continue;
 
-        __update_runq_load(ops, st.orqd, 0, now);
+        /* Use a value of NOW() sampled after taking orqd's lock. */
+        __update_runq_load(ops, st.orqd, 0, NOW());
     
         delta = st.lrqd->b_avgload - st.orqd->b_avgload;
         if ( delta < 0 )
@@ -1435,6 +1436,8 @@ retry:
     if ( unlikely(st.orqd->id < 0) )
         goto out_up;
 
+    now = NOW();
+
     /* Look for "swap" which gives the best load average
      * FIXME: O(n^2)! */
 


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  parent reply	other threads:[~2016-06-17 23:12 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-17 23:11 [PATCH 00/19] xen: sched: assorted fixes and improvements to Credit2 Dario Faggioli
2016-06-17 23:11 ` [PATCH 01/19] xen: sched: leave CPUs doing tasklet work alone Dario Faggioli
2016-06-20  7:48   ` Jan Beulich
2016-07-07 10:11     ` Dario Faggioli
2016-06-21 16:17   ` anshul makkar
2016-07-06 15:41   ` George Dunlap
2016-07-07 10:25     ` Dario Faggioli
2016-06-17 23:11 ` [PATCH 02/19] xen: sched: make the 'tickled' perf counter clearer Dario Faggioli
2016-06-18  0:36   ` Meng Xu
2016-07-06 15:52   ` George Dunlap
2016-06-17 23:11 ` [PATCH 03/19] xen: credit2: insert and tickle don't need a cpu parameter Dario Faggioli
2016-06-21 16:41   ` anshul makkar
2016-07-06 15:59   ` George Dunlap
2016-06-17 23:11 ` [PATCH 04/19] xen: credit2: kill useless helper function choose_cpu Dario Faggioli
2016-07-06 16:02   ` George Dunlap
2016-07-07 10:26     ` Dario Faggioli
2016-06-17 23:11 ` [PATCH 05/19] xen: credit2: do not warn if calling burn_credits more than once Dario Faggioli
2016-07-06 16:05   ` George Dunlap
2016-06-17 23:12 ` Dario Faggioli [this message]
2016-06-20  7:56   ` [PATCH 06/19] xen: credit2: read NOW() with the proper runq lock held Jan Beulich
2016-07-06 16:10     ` George Dunlap
2016-07-07 10:28       ` Dario Faggioli
2016-06-17 23:12 ` [PATCH 07/19] xen: credit2: prevent load balancing to go mad if time goes backwards Dario Faggioli
2016-06-20  8:02   ` Jan Beulich
2016-07-06 16:21     ` George Dunlap
2016-07-07  7:29       ` Jan Beulich
2016-07-07  9:09         ` George Dunlap
2016-07-07  9:18           ` Jan Beulich
2016-07-07 10:53             ` Dario Faggioli
2016-06-17 23:12 ` [PATCH 08/19] xen: credit2: when tickling, check idle cpus first Dario Faggioli
2016-07-06 16:36   ` George Dunlap
2016-06-17 23:12 ` [PATCH 09/19] xen: credit2: avoid calling __update_svc_load() multiple times on the same vcpu Dario Faggioli
2016-07-06 16:40   ` George Dunlap
2016-06-17 23:12 ` [PATCH 10/19] xen: credit2: rework load tracking logic Dario Faggioli
2016-07-06 17:33   ` George Dunlap
2016-06-17 23:12 ` [PATCH 11/19] tools: tracing: adapt Credit2 load tracking events to new format Dario Faggioli
2016-06-21  9:27   ` Wei Liu
2016-06-17 23:12 ` [PATCH 12/19] xen: credit2: use non-atomic cpumask and bit operations Dario Faggioli
2016-07-07  9:45   ` George Dunlap
2016-06-17 23:12 ` [PATCH 13/19] xen: credit2: make the code less experimental Dario Faggioli
2016-06-20  8:13   ` Jan Beulich
2016-07-07 10:59     ` Dario Faggioli
2016-07-07 15:17   ` George Dunlap
2016-07-07 16:43     ` Dario Faggioli
2016-06-17 23:12 ` [PATCH 14/19] xen: credit2: add yet some more tracing Dario Faggioli
2016-06-20  8:15   ` Jan Beulich
2016-07-07 15:34     ` George Dunlap
2016-07-07 15:34   ` George Dunlap
2016-06-17 23:13 ` [PATCH 15/19] xen: credit2: only marshall trace point arguments if tracing enabled Dario Faggioli
2016-07-07 15:37   ` George Dunlap
2016-06-17 23:13 ` [PATCH 16/19] tools: tracing: deal with new Credit2 events Dario Faggioli
2016-07-07 15:39   ` George Dunlap
2016-06-17 23:13 ` [PATCH 17/19] xen: credit2: the private scheduler lock can be an rwlock Dario Faggioli
2016-07-07 16:00   ` George Dunlap
2016-06-17 23:13 ` [PATCH 18/19] xen: credit2: implement SMT support independent runq arrangement Dario Faggioli
2016-06-20  8:26   ` Jan Beulich
2016-06-20 10:38     ` Dario Faggioli
2016-06-27 15:20   ` anshul makkar
2016-07-12 13:40   ` George Dunlap
2016-06-17 23:13 ` [PATCH 19/19] xen: credit2: use cpumask_first instead of cpumask_any when choosing cpu Dario Faggioli
2016-06-20  8:30   ` Jan Beulich
2016-06-20 11:28     ` Dario Faggioli
2016-06-21 10:42   ` David Vrabel
2016-07-07 16:55     ` Dario Faggioli

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