Commit 04971e82 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Luis Henriques

sched/autogroup: Fix failure to set cpu.rt_runtime_us

commit 1fe89e1b 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: default avatarZefan Li <lizefan@huawei.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Stefan Bader <stefan.bader@canonical.com>
Fixes: 8323f26c ("sched: Fix race in task_group()")
Link: http://lkml.kernel.org/r/20150209112237.GR5029@twins.programming.kicks-ass.netSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent 92a2a8f2
......@@ -87,8 +87,7 @@ 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;
......@@ -115,9 +114,6 @@ bool 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.
......
......@@ -7348,6 +7348,12 @@ 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) && task_rq(p)->rt.tg == tg)
return 1;
......
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