[PATCH pm-freezer 2/4] freezer: set PF_NOFREEZE on a dying task right before TASK_DEAD setting bug in freezer_change_state()

Tejun Heo tj at kernel.org
Wed Aug 31 03:21:43 PDT 2011

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 at kernel.org>
Reported-by: Oleg Nesterov <oleg at redhat.com>
Cc: "Rafael J. Wysocki" <rjw at sisk.pl>
 kernel/exit.c |   10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

Index: work/kernel/exit.c
--- work.orig/kernel/exit.c
+++ work/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;
@@ -1044,6 +1038,10 @@ NORET_TYPE void do_exit(long code)
+	/* 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;

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