From: Michal Koutný mkoutny@suse.com
[ Upstream commit 2630cde26711dab0d0b56a8be1616475be646d13 ]
Since commit a7b359fc6a37 ("sched/fair: Correctly insert cfs_rq's to list on unthrottle") we add cfs_rqs with no runnable tasks but not fully decayed into the load (leaf) list. We may ignore adding some ancestors and therefore breaking tmp_alone_branch invariant. This broke LTP test cfs_bandwidth01 and it was partially fixed in commit fdaba61ef8a2 ("sched/fair: Ensure that the CFS parent is added after unthrottling").
I noticed the named test still fails even with the fix (but with low probability, 1 in ~1000 executions of the test). The reason is when bailing out of unthrottle_cfs_rq early, we may miss adding ancestors of the unthrottled cfs_rq, thus, not joining tmp_alone_branch properly.
Fix this by adding ancestors if we notice the unthrottled cfs_rq was added to the load list.
Fixes: a7b359fc6a37 ("sched/fair: Correctly insert cfs_rq's to list on unthrottle") Signed-off-by: Michal Koutný mkoutny@suse.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Vincent Guittot vincent.guittot@linaro.org Reviewed-by: Odin Ugedal odin@uged.al Link: https://lore.kernel.org/r/20210917153037.11176-1-mkoutny@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/fair.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 30a6984a58f7..423ec671a306 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4898,8 +4898,12 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq) /* update hierarchical throttle state */ walk_tg_tree_from(cfs_rq->tg, tg_nop, tg_unthrottle_up, (void *)rq);
- if (!cfs_rq->load.weight) + /* Nothing to run but something to decay (on_list)? Complete the branch */ + if (!cfs_rq->load.weight) { + if (cfs_rq->on_list) + goto unthrottle_throttle; return; + }
task_delta = cfs_rq->h_nr_running; idle_task_delta = cfs_rq->idle_h_nr_running;