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Subject[PATCH 10/17] freezer: test freezable conditions while holding freezer_lock
Date
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>
---
kernel/freezer.c | 3 ++-
kernel/power/process.c | 16 +---------------
2 files changed, 3 insertions(+), 16 deletions(-)
diff --git a/kernel/freezer.c b/kernel/freezer.c
index 05afd68..5c911c0 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 e6e2739..e59676f 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;

--
1.7.3.1


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