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Commit 000b8949 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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

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()
parents 7cfc4317 8e5bfa8c

include/linux/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -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_fork(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

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);
@@ -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_fork(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



extern int yield_to(struct task_struct *p, bool preempt);

kernel/exit.c

+1 −0
Original line number Diff line number Diff line
@@ -836,6 +836,7 @@ void __noreturn do_exit(long code) 
	 */

	perf_event_exit_task(tsk);



	sched_autogroup_exit_task(tsk);

	cgroup_exit(tsk);



	/*

kernel/sched/auto_group.c

+28 −8
Original line number Diff line number Diff line
@@ -111,10 +111,13 @@ bool task_wants_autogroup(struct task_struct *p, struct task_group *tg) 
{

	if (tg != &root_task_group)

		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.

	 * If we race with autogroup_move_group() the caller can use the old

	 * 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)

		return false;
@@ -122,6 +125,16 @@ bool task_wants_autogroup(struct task_struct *p, struct task_group *tg) 
	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

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);



	if (!READ_ONCE(sysctl_sched_autogroup_enabled))

		goto out;



	/*

	 * We can't avoid sched_move_task() after we changed signal->autogroup,

	 * 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)

		sched_move_task(t);

out:



	unlock_task_sighand(p, &flags);

	autogroup_kref_put(prev);

}