Commit-ID: 8e5bfa8c1f8471aa4a2d30be631ef2b50e10abaf
Gitweb: http://git.kernel.org/tip/8e5bfa8c1f8471aa4a2d30be631ef2b50e10abaf
Author: Oleg Nesterov <oleg@xxxxxxxxxx>
AuthorDate: Mon, 14 Nov 2016 19:46:12 +0100
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 22 Nov 2016 12:33:43 +0100
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: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: hartsjc@xxxxxxxxxx
Cc: vbendel@xxxxxxxxxx
Cc: vlovejoy@xxxxxxxxxx
Link: http://lkml.kernel.org/r/20161114184612.GA15968@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
include/linux/sched.h | 2 ++
kernel/exit.c | 1 +
kernel/sched/auto_group.c | 19 +++++++++++++++++++
3 files changed, 22 insertions(+)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 348f51b..e9c009d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -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);
diff --git a/kernel/exit.c b/kernel/exit.c
index 9d68c45..3076f30 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -836,6 +836,7 @@ void __noreturn do_exit(long code)
*/
perf_event_exit_task(tsk);
+ sched_autogroup_exit_task(tsk);
cgroup_exit(tsk);
/*
diff --git a/kernel/sched/auto_group.c b/kernel/sched/auto_group.c
index ad2b19a..f1c8fd5 100644
--- a/kernel/sched/auto_group.c
+++ b/kernel/sched/auto_group.c
@@ -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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