[SRU][noble:linux][PATCH 1/1] sched/eevdf: Prevent vlag from going out of bounds in reweight_eevdf()
John Cabaj
john.cabaj at canonical.com
Fri Jun 7 04:05:19 UTC 2024
From: Xuewen Yan <xuewen.yan at unisoc.com>
BugLink: https://bugs.launchpad.net/bugs/2068024
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@nz.home/
Closes: https://lore.kernel.org/all/CA+9S74ih+45M_2TPUY_mPPVDhNvyYfy1J1ftSix+KjiTVxg8nw@mail.gmail.com/
Closes: https://lore.kernel.org/lkml/202401301012.2ed95df0-oliver.sang@intel.com/
Fixes: eab03c23c2a1 ("sched/eevdf: Fix vruntime adjustment on reweight")
Reported-by: Sergei Trofimovich <slyich at gmail.com>
Reported-by: Igor Raits <igor at gooddata.com>
Reported-by: Breno Leitao <leitao at debian.org>
Reported-by: kernel test robot <oliver.sang at intel.com>
Reported-by: Yujie Liu <yujie.liu at intel.com>
Signed-off-by: Xuewen Yan <xuewen.yan at unisoc.com>
Reviewed-and-tested-by: Chen Yu <yu.c.chen at intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
Link: https://lore.kernel.org/r/20240422082238.5784-1-xuewen.yan@unisoc.com
(cherry picked from commit 1560d1f6eb6b398bddd80c16676776c0325fe5fe)
Signed-off-by: John Cabaj <john.cabaj at canonical.com>
---
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 e2b4e0396af8..4129ee7627de 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);
}
/*
@@ -3755,7 +3761,7 @@ static void reweight_eevdf(struct cfs_rq *cfs_rq, struct sched_entity *se,
* = 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;
}
--
2.34.1
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