lkml.org 
[lkml]   [2024]   [Apr]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v2] sched/eevdf: Prevent vlag from going out of bounds when reweight_eevdf
Date
kernel encounters the following error when running workload:

BUG: kernel NULL pointer dereference, address: 0000002c
EIP: set_next_entity (fair.c:?)

which was caused by NULL pointer returned by pick_eevdf().

Further investigation has shown that, the entity_eligible() has an
false-negative issue when the entity's vruntime is far behind the
cfs_rq.min_vruntime that, the (vruntime - cfs_rq->min_vruntime) * load
caused a s64 overflow, thus every entity on the rb-tree is not
eligible, which results in a NULL candidate.

The reason why entity's vruntime is far behind the cfs_rq.min_vruntime
is because during a on_rq task group's update_cfs_group()->reweight_eevdf(),
there is no limit on the new entity's vlag. If the new weight is much
smaller than the old one,

vlag = div_s64(vlag * old_weight, weight)

generates a huge vlag, and results in very small(negative) vruntime.

Thus limit the range of vlag accordingly.

Reported-by: Sergei Trofimovich <slyich@gmail.com>
Closes: https://lore.kernel.org/all/ZhuYyrh3mweP_Kd8@nz.home/
Reported-by: Igor Raits <igor@gooddata.com>
Closes: https://lore.kernel.org/all/CA+9S74ih+45M_2TPUY_mPPVDhNvyYfy1J1ftSix+KjiTVxg8nw@mail.gmail.com/
Reported-by: Breno Leitao <leitao@debian.org>
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/lkml/202401301012.2ed95df0-oliver.sang@intel.com/
Reported-by: Yujie Liu <yujie.liu@intel.com>
Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>
---
changes of v2:
-add reported-by (suggested by <yu.c.chen@intel.com>)
-remork the changelog (<yu.c.chen@intel.com>)
-remove the judgement of fork (Peter)
-remove the !on_rq case. (Peter)
---
Previous discussion link:
https://lore.kernel.org/lkml/20240226082349.302363-1-yu.c.chen@intel.com/
https://lore.kernel.org/all/20240130080643.1828-1-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 03be0d1330a6..64826f406d6d 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);
}

/*
@@ -3761,7 +3767,7 @@ 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;
}
--
2.25.1

\
 
 \ /
  Last update: 2024-05-27 17:55    [W:0.092 / U:0.540 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site