From 1560d1f6eb6b398bddd80c16676776c0325fe5fe Mon Sep 17 00:00:00 2001 From: Xuewen Yan Date: Mon, 22 Apr 2024 16:22:38 +0800 Subject: 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@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 Reported-by: Igor Raits Reported-by: Breno Leitao Reported-by: kernel test robot Reported-by: Yujie Liu Signed-off-by: Xuewen Yan Reviewed-and-tested-by: Chen Yu Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20240422082238.5784-1-xuewen.yan@unisoc.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 6d266917d38d7f..c62805dbd6088b 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; } -- cgit 1.2.3-korg