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Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

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Pull scheduler fixes from Ingo Molnar:
 "Two fixes for autogroup scheduling, for races when turning the feature
  on/off via /proc/sys/kernel/sched_autogroup_enabled"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/autogroup: Do not use autogroup->tg in zombie threads
  sched/autogroup: Fix autogroup_move_group() to never skip sched_move_task()
This commit is contained in:
Linus Torvalds 2016-11-22 12:51:35 -08:00
commit 000b8949e9
3 changed files with 31 additions and 8 deletions
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2
include/linux/sched.h
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@ -2567,6 +2567,7 @@ extern void sched_autogroup_create_attach(struct task_struct *p);
extern void sched_autogroup_detach(struct task_struct *p); extern void sched_autogroup_detach(struct task_struct *p);
extern void sched_autogroup_fork(struct signal_struct *sig); extern void sched_autogroup_fork(struct signal_struct *sig);
extern void sched_autogroup_exit(struct signal_struct *sig); extern void sched_autogroup_exit(struct signal_struct *sig);
extern void sched_autogroup_exit_task(struct task_struct *p);
#ifdef CONFIG_PROC_FS #ifdef CONFIG_PROC_FS
extern void proc_sched_autogroup_show_task(struct task_struct *p, struct seq_file *m); extern void proc_sched_autogroup_show_task(struct task_struct *p, struct seq_file *m);
extern int proc_sched_autogroup_set_nice(struct task_struct *p, int nice); extern int proc_sched_autogroup_set_nice(struct task_struct *p, int nice);
@ -2576,6 +2577,7 @@ static inline void sched_autogroup_create_attach(struct task_struct *p) { }
static inline void sched_autogroup_detach(struct task_struct *p) { } static inline void sched_autogroup_detach(struct task_struct *p) { }
static inline void sched_autogroup_fork(struct signal_struct *sig) { } static inline void sched_autogroup_fork(struct signal_struct *sig) { }
static inline void sched_autogroup_exit(struct signal_struct *sig) { } static inline void sched_autogroup_exit(struct signal_struct *sig) { }
static inline void sched_autogroup_exit_task(struct task_struct *p) { }
#endif #endif
extern int yield_to(struct task_struct *p, bool preempt); extern int yield_to(struct task_struct *p, bool preempt);

1
kernel/exit.c
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@ -836,6 +836,7 @@ void __noreturn do_exit(long code)
*/ */
perf_event_exit_task(tsk); perf_event_exit_task(tsk);
sched_autogroup_exit_task(tsk);
cgroup_exit(tsk); cgroup_exit(tsk);
/* /*

36
kernel/sched/auto_group.c
View File

@ -111,10 +111,13 @@ bool task_wants_autogroup(struct task_struct *p, struct task_group *tg)
{ {
if (tg != &root_task_group) if (tg != &root_task_group)
return false; return false;
/* /*
* We can only assume the task group can't go away on us if * If we race with autogroup_move_group() the caller can use the old
* autogroup_move_group() can see us on ->thread_group list. * value of signal->autogroup but in this case sched_move_task() will
* be called again before autogroup_kref_put().
*
* However, there is no way sched_autogroup_exit_task() could tell us
* to avoid autogroup->tg, so we abuse PF_EXITING flag for this case.
*/ */
if (p->flags & PF_EXITING) if (p->flags & PF_EXITING)
return false; return false;
@ -122,6 +125,16 @@ bool task_wants_autogroup(struct task_struct *p, struct task_group *tg)
return true; return true;
} }
void sched_autogroup_exit_task(struct task_struct *p)
{
/*
* We are going to call exit_notify() and autogroup_move_group() can't
* see this thread after that: we can no longer use signal->autogroup.
* See the PF_EXITING check in task_wants_autogroup().
*/
sched_move_task(p);
}
static void static void
autogroup_move_group(struct task_struct *p, struct autogroup *ag) autogroup_move_group(struct task_struct *p, struct autogroup *ag)
{ {
@ -138,13 +151,20 @@ autogroup_move_group(struct task_struct *p, struct autogroup *ag)
} }
p->signal->autogroup = autogroup_kref_get(ag); p->signal->autogroup = autogroup_kref_get(ag);
/*
if (!READ_ONCE(sysctl_sched_autogroup_enabled)) * We can't avoid sched_move_task() after we changed signal->autogroup,
goto out; * this process can already run with task_group() == prev->tg or we can
* race with cgroup code which can read autogroup = prev under rq->lock.
* In the latter case for_each_thread() can not miss a migrating thread,
* cpu_cgroup_attach() must not be possible after cgroup_exit() and it
* can't be removed from thread list, we hold ->siglock.
*
* If an exiting thread was already removed from thread list we rely on
* sched_autogroup_exit_task().
*/
for_each_thread(p, t) for_each_thread(p, t)
sched_move_task(t); sched_move_task(t);
out:
unlock_task_sighand(p, &flags); unlock_task_sighand(p, &flags);
autogroup_kref_put(prev); autogroup_kref_put(prev);
} }