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Subject[PATCH 2/6] freezer: set PF_NOFREEZE on a dying task right before TASK_DEAD setting bug in freezer_change_state()
Date
3fb45733df "freezer: make exiting tasks properly unfreezable" removed
clear_freeze_flag() from exit path and set PF_NOFREEZE right after
PTRACE_EVENT_EXIT; however, Oleg pointed out that following exit paths
may cause interaction with device drivers after PM freezer consider
the system frozen.

There's no try_to_freeze() call in the exit path and the only
necessary guarantee is that freezer doesn't hang waiting for zombies.
Set PF_NOFREEZE right before setting tsk->state to TASK_DEAD instead.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Oleg Nesterov <oleg@redhat.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
---
kernel/exit.c | 10 ++++------
1 files changed, 4 insertions(+), 6 deletions(-)
diff --git a/kernel/exit.c b/kernel/exit.c
index ac58259..7b6c4fa 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -913,12 +913,6 @@ NORET_TYPE void do_exit(long code)

ptrace_event(PTRACE_EVENT_EXIT, code);

- /*
- * With ptrace notification done, there's no point in freezing from
- * here on. Disallow freezing.
- */
- current->flags |= PF_NOFREEZE;
-
validate_creds_for_do_exit(tsk);

/*
@@ -1044,6 +1038,10 @@ NORET_TYPE void do_exit(long code)

preempt_disable();
exit_rcu();
+
+ /* this task is now dead and freezer should ignore it */
+ current->flags |= PF_NOFREEZE;
+
/* causes final put_task_struct in finish_task_switch(). */
tsk->state = TASK_DEAD;
schedule();
--
1.7.6


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