The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: 1560d1f6eb6b398bddd80c16676776c0325fe5fe
Gitweb: https://git.kernel.org/tip/1560d1f6eb6b398bddd80c16676776c0325fe5fe
Author: Xuewen Yan <xuewen.yan@xxxxxxxxxx>
AuthorDate: Mon, 22 Apr 2024 16:22:38 +08:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 22 Apr 2024 13:01:27 +02:00
sched/eevdf: Prevent vlag from going out of bounds in reweight_eevdf()
It was possible to have pick_eevdf() return NULL, which then causes a
NULL-deref. This turned out to be due to entity_eligible() returning
falsely negative because of a s64 multiplcation overflow.
Specifically, reweight_eevdf() computes the vlag without considering
the limit placed upon vlag as update_entity_lag() does, and then the
scaling multiplication (remember that weight is 20bit fixed point) can
overflow. This then leads to the new vruntime being weird which then
causes the above entity_eligible() to go side-ways and claim nothing
is eligible.
Thus limit the range of vlag accordingly.
All this was quite rare, but fatal when it does happen.
Closes: https://lore.kernel.org/all/ZhuYyrh3mweP_Kd8@xxxxxxx/
Closes: https://lore.kernel.org/all/CA+9S74ih+45M_2TPUY_mPPVDhNvyYfy1J1ftSix+KjiTVxg8nw@xxxxxxxxxxxxxx/
Closes: https://lore.kernel.org/lkml/202401301012.2ed95df0-oliver.sang@xxxxxxxxx/
Fixes: eab03c23c2a1 ("sched/eevdf: Fix vruntime adjustment on reweight")
Reported-by: Sergei Trofimovich <slyich@xxxxxxxxx>
Reported-by: Igor Raits <igor@xxxxxxxxxxxx>
Reported-by: Breno Leitao <leitao@xxxxxxxxxx>
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Reported-by: Yujie Liu <yujie.liu@xxxxxxxxx>
Signed-off-by: Xuewen Yan <xuewen.yan@xxxxxxxxxx>
Reviewed-and-tested-by: Chen Yu <yu.c.chen@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240422082238.5784-1-xuewen.yan@xxxxxxxxxx
---
kernel/sched/fair.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6d26691..c62805d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -696,15 +696,21 @@ u64 avg_vruntime(struct cfs_rq *cfs_rq)
*
* XXX could add max_slice to the augmented data to track this.
*/
-static void update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se)
+static s64 entity_lag(u64 avruntime, struct sched_entity *se)
{
- s64 lag, limit;
+ s64 vlag, limit;
+
+ vlag = avruntime - se->vruntime;
+ limit = calc_delta_fair(max_t(u64, 2*se->slice, TICK_NSEC), se);
+
+ return clamp(vlag, -limit, limit);
+}
+static void update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se)
+{
SCHED_WARN_ON(!se->on_rq);
- lag = avg_vruntime(cfs_rq) - se->vruntime;
- limit = calc_delta_fair(max_t(u64, 2*se->slice, TICK_NSEC), se);
- se->vlag = clamp(lag, -limit, limit);
+ se->vlag = entity_lag(avg_vruntime(cfs_rq), se);
}
/*
@@ -3760,7 +3766,7 @@ static void reweight_eevdf(struct sched_entity *se, u64 avruntime,
* = V - vl'
*/
if (avruntime != se->vruntime) {
- vlag = (s64)(avruntime - se->vruntime);
+ vlag = entity_lag(avruntime, se);
vlag = div_s64(vlag * old_weight, weight);
se->vruntime = avruntime - vlag;
}
|