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authorVincent Guittot <vincent.guittot@linaro.org>2019-01-30 06:22:47 +0100
committerIngo Molnar <mingo@kernel.org>2019-02-04 09:14:48 +0100
commitf6783319737f28e4436a69611853a5a098cbe974 (patch)
treeec66296ed1f42194c8913318393dea5d3176e6d0 /init
parent5d299eabea5a251fbf66e8277704b874bbba92dc (diff)
downloadlinux-f6783319737f28e4436a69611853a5a098cbe974.tar.bz2
sched/fair: Fix insertion in rq->leaf_cfs_rq_list
Sargun reported a crash: "I picked up c40f7d74c741a907cfaeb73a7697081881c497d0 sched/fair: Fix infinite loop in update_blocked_averages() by reverting a9e7f6544b9c and put it on top of 4.19.13. In addition to this, I uninlined list_add_leaf_cfs_rq for debugging. This revealed a new bug that we didn't get to because we kept getting crashes from the previous issue. When we are running with cgroups that are rapidly changing, with CFS bandwidth control, and in addition using the cpusets cgroup, we see this crash. Specifically, it seems to occur with cgroups that are throttled and we change the allowed cpuset." The algorithm used to order cfs_rq in rq->leaf_cfs_rq_list assumes that it will walk down to root the 1st time a cfs_rq is used and we will finish to add either a cfs_rq without parent or a cfs_rq with a parent that is already on the list. But this is not always true in presence of throttling. Because a cfs_rq can be throttled even if it has never been used but other CPUs of the cgroup have already used all the bandwdith, we are not sure to go down to the root and add all cfs_rq in the list. Ensure that all cfs_rq will be added in the list even if they are throttled. [ mingo: Fix !CGROUPS build. ] Reported-by: Sargun Dhillon <sargun@sargun.me> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: tj@kernel.org Fixes: 9c2791f936ef ("Fix hierarchical order in rq->leaf_cfs_rq_list") Link: https://lkml.kernel.org/r/1548825767-10799-1-git-send-email-vincent.guittot@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
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