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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>
This commit is contained in:
Tejun Heo 2011-11-21 12:32:24 -08:00
parent 6907483b4e
commit 85f1d47665
2 changed files with 3 additions and 16 deletions
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3
kernel/freezer.c
View File

@ -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))

16
kernel/power/process.c
View File

@ -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;