6.8-stable review patch. If anyone has any objections, please let me know.
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From: Xuewen Yan xuewen.yan@unisoc.com
[ Upstream commit 1560d1f6eb6b398bddd80c16676776c0325fe5fe ]
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+KjiTVxg... 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@gmail.com Reported-by: Igor Raits igor@gooddata.com Reported-by: Breno Leitao leitao@debian.org Reported-by: kernel test robot oliver.sang@intel.com Reported-by: Yujie Liu yujie.liu@intel.com Signed-off-by: Xuewen Yan xuewen.yan@unisoc.com Reviewed-and-tested-by: Chen Yu yu.c.chen@intel.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lore.kernel.org/r/20240422082238.5784-1-xuewen.yan@unisoc.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 b9ee4397b484a..aee5e7a70170c 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); }
/* @@ -3754,7 +3760,7 @@ 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; }