Messages in this thread | | | Subject | Re: [PATCH 1/2] sched/cgroup: move sched_online_group() back into css_online() | From | Konstantin Khlebnikov <> | Date | Thu, 26 Jan 2017 13:27:21 +0300 |
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On 26.01.2017 13:17, Peter Zijlstra wrote: > On Thu, Jan 26, 2017 at 12:41:41PM +0300, Konstantin Khlebnikov wrote: >> Commit 2f5177f0fd7e ("sched/cgroup: Fix/cleanup cgroup teardown/init") moved >> sched_online_group() from css_online() to css_alloc(). It exposes half-baked >> task group into global lists before initializing generic cgroup stuff. >> >> LTP testcase (third in cgroup_regression_test) written for testing >> similar race in kernels 2.6.26-2.6.28 easily triggers this oops: >> > > So nobody's run LTP against the kernel for almost a year?
Yep. Nobody runs LTP =)
CONFIG_RT_GROUP_SCHED must be y (which almost impossible to use IRL, I have some patches for it out of tree)
Also systemd by default binds cgroups cpu and cpuacct together - this breaks testcase.
> >> >> Here task group already linked into global RCU-protected list task_groups >> but pointer css->cgroup is still NULL. >> >> This patch reverts this chunk and moves online back to css_online(). > > Maybe put a comment with it that explains why this is needed? > > Something along the lines of this perhaps? >
Actually online is called before complete initialization. See second patch. =) I don't know what to do with this. cgroups are messy as always.
> /* > * Don't expose the cgroup until initialization of it is complete in the > * cgroup core. Otherwise things like cgroup_path() will return NULL > * pointers and the like. > */ > >> +static int cpu_cgroup_css_online(struct cgroup_subsys_state *css) >> +{ >> + struct task_group *tg = css_tg(css); >> + struct task_group *parent = css_tg(css->parent); >> + >> + if (parent) >> + sched_online_group(tg, parent); >> + return 0; >> +}
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