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

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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: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Oleg Nesterov 2016-11-14 19:46:12 +01:00 committed by Ingo Molnar
parent 18f649ef34
commit 8e5bfa8c1f
3 changed files with 22 additions and 0 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

2
include/linux/sched.h
View file

@ -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);

1
kernel/exit.c
View file

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

19
kernel/sched/auto_group.c
View file

@ -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);