+ freezer-close-theoretical-race-between-refrigerator-and-thaw_tasks.patch added to -mm tree

[akpm@xxxxxxxxxxxxxxxxxxxx]

The patch titled
     freezer: close theoretical race between refrigerator and thaw_tasks
has been added to the -mm tree.  Its filename is
     freezer-close-theoretical-race-between-refrigerator-and-thaw_tasks.patch

*** Remember to use Documentation/SubmitChecklist when testing your code ***

See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this

------------------------------------------------------
Subject: freezer: close theoretical race between refrigerator and thaw_tasks
From: Rafael J. Wysocki <rjw@xxxxxxx>

If the freezing of tasks fails and a task is preempted in refrigerator()
before calling frozen_process(), then thaw_tasks() may run before this task is
frozen.  In that case the task will freeze and no one will thaw it.

To fix this race we can call freezing(current) in refrigerator() along with
frozen_process(current) under the task_lock() which also should be taken in
the error path of try_to_freeze_tasks() as well as in thaw_process(). 
Moreover, if thaw_process() additionally clears TIF_FREEZE for tasks that are
not frozen, we can be sure that all tasks are thawed and there are no pending
"freeze" requests after thaw_tasks() has run.

Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
Acked-by: Pavel Machek <pavel@xxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Aneesh Kumar <aneesh.kumar@xxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Srivatsa Vaddagiri <vatsa@xxxxxxxxxx>
Cc: Gautham R Shenoy <ego@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 include/linux/freezer.h |    4 ++++
 kernel/power/process.c  |   12 +++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff -puN include/linux/freezer.h~freezer-close-theoretical-race-between-refrigerator-and-thaw_tasks include/linux/freezer.h
--- a/include/linux/freezer.h~freezer-close-theoretical-race-between-refrigerator-and-thaw_tasks
+++ a/include/linux/freezer.h
@@ -40,11 +40,15 @@ static inline void do_not_freeze(struct 
  */
 static inline int thaw_process(struct task_struct *p)
 {
+	task_lock(p);
 	if (frozen(p)) {
 		p->flags &= ~PF_FROZEN;
+		task_unlock(p);
 		wake_up_process(p);
 		return 1;
 	}
+	clear_tsk_thread_flag(p, TIF_FREEZE);
+	task_unlock(p);
 	return 0;
 }
 
diff -puN kernel/power/process.c~freezer-close-theoretical-race-between-refrigerator-and-thaw_tasks kernel/power/process.c
--- a/kernel/power/process.c~freezer-close-theoretical-race-between-refrigerator-and-thaw_tasks
+++ a/kernel/power/process.c
@@ -39,10 +39,18 @@ void refrigerator(void)
 	/* Hmm, should we be allowed to suspend when there are realtime
 	   processes around? */
 	long save;
+
+	task_lock(current);
+	if (freezing(current)) {
+		frozen_process(current);
+		task_unlock(current);
+	} else {
+		task_unlock(current);
+		return;
+	}
 	save = current->state;
 	pr_debug("%s entered refrigerator\n", current->comm);
 
-	frozen_process(current);
 	spin_lock_irq(&current->sighand->siglock);
 	recalc_sigpending(); /* We sent fake signal, clean it up */
 	spin_unlock_irq(&current->sighand->siglock);
@@ -159,10 +167,12 @@ static unsigned int try_to_freeze_tasks(
 			if (is_user_space(p) == !freeze_user_space)
 				continue;
 
+			task_lock(p);
 			if (freezeable(p) && !frozen(p))
 				printk(KERN_ERR " %s\n", p->comm);
 
 			cancel_freezing(p);
+			task_unlock(p);
 		} while_each_thread(g, p);
 		read_unlock(&tasklist_lock);
 	}
_

Patches currently in -mm which might be from rjw@xxxxxxx are

make-xfs-workqueues-nonfreezable.patch
fix-refrigerator-vs-thaw_process-race.patch
freezer-task-exit_state-should-be-treated-as-bolean.patch
documentation-ask-driver-writers-to-provide-pm-support.patch
freezer-read-pf_borrowed_mm-in-a-nonracy-way.patch
freezer-close-theoretical-race-between-refrigerator-and-thaw_tasks.patch
freezer-remove-pf_nofreeze-from-rcutorture-thread.patch
freezer-remove-pf_nofreeze-from-bluetooth-threads.patch
freezer-add-try_to_freeze-calls-to-all-kernel-threads.patch
freezer-fix-vfork-problem.patch
freezer-take-kernel_execve-into-consideration.patch
shrink_slab-handle-bad-shrinkers.patch

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