Current code reads cp->elements[0].cpu and cp->elements[0].dl without
acquiring cpudl's lock. There are two problems on it:
1. When we read elements[0].dl, the value can be broken on 32 bit
machine because elements[0].dl is 64 bit data. We should guarantee
it to be done atomically.
2. Obsolete data can be read unless syncronizing with updaters:
updater1 updater2 reader
-------- -------- ------
lock A
set maxcpu = cpu1
unlock A
lock A
set maxcpu = cpu2
unlock A
read maxcpu, it might be -1
where maxcpu was -1 initially.
When reading maxcpu, the value might be -1, we expect that should be
cpu2 though. So force readers also to be protected using the lock.
Signed-off-by: Byungchul Park <byungchul.p...@lge.com>
---
kernel/sched/cpudeadline.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c
index f03479c..37bbb66 100644
--- a/kernel/sched/cpudeadline.c
+++ b/kernel/sched/cpudeadline.c
@@ -118,8 +118,14 @@ static inline u64 cpudl_maximum_dl(struct cpudl *cp)
static int cpudl_fast_find(struct cpudl *cp, struct task_struct *p)
{
const struct sched_dl_entity *dl_se = &p->dl;
- int max_cpu = cpudl_maximum_cpu(cp);
- u64 max_dl = cpudl_maximum_dl(cp);
+ unsigned long flags;
+ int max_cpu;
+ u64 max_dl;
+
+ raw_spin_lock_irqsave(&cp->lock, flags);
+ max_cpu = cpudl_maximum_cpu(cp);
+ max_dl = cpudl_maximum_dl(cp);
+ raw_spin_unlock_irqrestore(&cp->lock, flags);
if (cpumask_test_cpu(max_cpu, &p->cpus_allowed) &&
dl_time_before(dl_se->deadline, max_dl))
--
1.9.1
