sched/fair: Ensure that the CFS parent is added after unthrottling
Ensure that a CFS parent will be in the list whenever one of its children is also in the list. A warning on rq->tmp_alone_branch != &rq->leaf_cfs_rq_list has been reported while running LTP test cfs_bandwidth01. Odin Ugedal found the root cause: $ tree /sys/fs/cgroup/ltp/ -d --charset=ascii /sys/fs/cgroup/ltp/ |-- drain `-- test-6851 `-- level2 |-- level3a | |-- worker1 | `-- worker2 `-- level3b `-- worker3 Timeline (ish): - worker3 gets throttled - level3b is decayed, since it has no more load - level2 get throttled - worker3 get unthrottled - level2 get unthrottled - worker3 is added to list - level3b is not added to list, since nr_running==0 and is decayed [ Vincent Guittot: Rebased and updated to fix for the reported warning. ] Fixes: a7b359fc ("sched/fair: Correctly insert cfs_rq's to list on unthrottle") Reported-by:Sachin Sant <sachinp@linux.vnet.ibm.com> Suggested-by:
Vincent Guittot <vincent.guittot@linaro.org> Signed-off-by:
Rik van Riel <riel@surriel.com> Signed-off-by:
Vincent Guittot <vincent.guittot@linaro.org> Signed-off-by:
Ingo Molnar <mingo@kernel.org> Tested-by:
Sachin Sant <sachinp@linux.vnet.ibm.com> Acked-by:
Odin Ugedal <odin@uged.al> Link: https://lore.kernel.org/r/20210621174330.11258-1-vincent.guittot@linaro.org
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