Commit 8e5bfa8c authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Ingo Molnar
Browse files

sched/autogroup: Do not use autogroup->tg in zombie threads 



Exactly because for_each_thread() in autogroup_move_group() can't see it
and update its ->sched_task_group before _put() and possibly free().

So the exiting task needs another sched_move_task() before exit_notify()
and we need to re-introduce the PF_EXITING (or similar) check removed by
the previous change for another reason.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: hartsjc@redhat.com
Cc: vbendel@redhat.com
Cc: vlovejoy@redhat.com
Link: http://lkml.kernel.org/r/20161114184612.GA15968@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 18f649ef

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

+19 −0
Original line number Diff line number Diff line
@@ -115,10 +115,26 @@ bool task_wants_autogroup(struct task_struct *p, struct task_group *tg) 
	 * 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;



	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)

{
@@ -142,6 +158,9 @@ autogroup_move_group(struct task_struct *p, struct autogroup *ag) 
	 * 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);

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