freezer: test freezable conditions while holding freezer_lock

try_to_freeze_tasks() and thaw_processes() use freezable() and
frozen() as preliminary tests before initiating operations on a task.
These are done without any synchronization and hinder with
synchronization cleanup without any real performance benefits.

In try_to_freeze_tasks(), open code self test and move PF_NOFREEZE and
frozen() tests inside freezer_lock in freeze_task().

thaw_processes() can simply drop freezable() test as frozen() test in
__thaw_task() is enough.

Note: This used to be a part of larger patch to fix set_freezable()
      race.  Separated out to satisfy ordering among dependent fixes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>

2 files changed, 3 insertions, 16 deletions

diff --git a/kernel/freezer.c b/kernel/freezer.c
index a8822be43da0..a257ecd37c48 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -109,7 +109,8 @@ bool freeze_task(struct task_struct *p, bool sig_only)
 
         spin_lock_irqsave(&freezer_lock, flags);
 
-        if (sig_only && !should_send_signal(p))
+        if ((p->flags & PF_NOFREEZE) ||
+            (sig_only && !should_send_signal(p)))
                 goto out_unlock;
 
         if (frozen(p))
diff --git a/kernel/power/process.c b/kernel/power/process.c
index e6e2739190b5..e59676f5811d 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -22,14 +22,6 @@
  */
 #define TIMEOUT (20 * HZ)
 
-static inline int freezable(struct task_struct * p)
-{
-        if ((p == current) ||
-            (p->flags & PF_NOFREEZE))
-                return 0;
-        return 1;
-}
-
 static int try_to_freeze_tasks(bool sig_only)
 {
         struct task_struct *g, *p;
@@ -52,10 +44,7 @@ static int try_to_freeze_tasks(bool sig_only)
                 todo = 0;
                 read_lock(&tasklist_lock);
                 do_each_thread(g, p) {
-                        if (frozen(p) || !freezable(p))
-                                continue;
-
-                        if (!freeze_task(p, sig_only))
+                        if (p == current || !freeze_task(p, sig_only))
                                 continue;
 
                         /*
@@ -181,9 +170,6 @@ void thaw_processes(void)
 
         read_lock(&tasklist_lock);
         do_each_thread(g, p) {
-                if (!freezable(p))
-                        continue;
-
                 if (cgroup_freezing_or_frozen(p))
                         continue;