From 59c51ae041f69c207ec77ff836be3b59f8a74472 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 9 Feb 2015 11:53:18 +0100 Subject: [PATCH 1/1] sched/autogroup: Fix failure to set cpu.rt_runtime_us commit 1fe89e1b6d270aa0d3452c60d38461ea589594e3 upstream. Because task_group() uses a cache of autogroup_task_group(), whose output depends on sched_class, switching classes can generate problems. In particular, when started as fair, the cache points to the autogroup, so when switching to RT the tg_rt_schedulable() test fails for every cpu.rt_{runtime,period}_us change because now the autogroup has tasks and no runtime. Furthermore, going back to the previous semantics of varying task_group() with sched_class has the down-side that the sched_debug output varies as well, even though the task really is in the autogroup. Therefore add an autogroup exception to tg_has_rt_tasks() -- such that both (all) task_group() usages in sched/core now have one. And remove all the remnants of the variable task_group() output. Reported-by: Zefan Li Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Mike Galbraith Cc: Stefan Bader Fixes: 8323f26ce342 ("sched: Fix race in task_group()") Link: http://lkml.kernel.org/r/20150209112237.GR5029@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar [bwh: Backported to 3.2: adjust filenames, context] Signed-off-by: Ben Hutchings --- kernel/sched.c | 6 ++++++ kernel/sched_autogroup.c | 6 +----- 2 files changed, 7 insertions(+), 5 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index ea85b0d2bbf2..29e5bf1e970a 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -9104,6 +9104,12 @@ static inline int tg_has_rt_tasks(struct task_group *tg) { struct task_struct *g, *p; + /* + * Autogroups do not have RT tasks; see autogroup_create(). + */ + if (task_group_is_autogroup(tg)) + return 0; + do_each_thread(g, p) { if (rt_task(p) && rt_rq_of_se(&p->rt)->tg == tg) return 1; diff --git a/kernel/sched_autogroup.c b/kernel/sched_autogroup.c index f280df1e550c..cb0a950681f6 100644 --- a/kernel/sched_autogroup.c +++ b/kernel/sched_autogroup.c @@ -86,8 +86,7 @@ static inline struct autogroup *autogroup_create(void) * so we don't have to move tasks around upon policy change, * or flail around trying to allocate bandwidth on the fly. * A bandwidth exception in __sched_setscheduler() allows - * the policy change to proceed. Thereafter, task_group() - * returns &root_task_group, so zero bandwidth is required. + * the policy change to proceed. */ free_rt_sched_group(tg); tg->rt_se = root_task_group.rt_se; @@ -114,9 +113,6 @@ task_wants_autogroup(struct task_struct *p, struct task_group *tg) if (tg != &root_task_group) return false; - if (p->sched_class != &fair_sched_class) - return false; - /* * We can only assume the task group can't go away on us if * autogroup_move_group() can see us on ->thread_group list. -- 2.39.2