freezer: fix vfork problem

Currently try_to_freeze_tasks() has to wait until all of the vforked processes
exit and for this reason every user can make it fail.  To fix this problem we
can introduce the additional process flag PF_FREEZER_SKIP to be used by tasks
that do not want to be counted as freezable by the freezer and want to have
TIF_FREEZE set nevertheless.  Then, this flag can be set by tasks using
sys_vfork() before they call wait_for_completion(&vfork) and cleared after
they have woken up.  After clearing it, the tasks should call try_to_freeze()
as soon as possible.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Gautham R Shenoy <ego@in.ibm.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a81897e2a244..870b75e348ab 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1182,6 +1182,7 @@ static inline void put_task_struct(struct task_struct *t)
 #define PF_SPREAD_SLAB  0x02000000      /* Spread some slab caches over cpuset */
 #define PF_MEMPOLICY    0x10000000      /* Non-default NUMA mempolicy */
 #define PF_MUTEX_TESTER 0x20000000      /* Thread belongs to the rt mutex tester */
+#define PF_FREEZER_SKIP 0x40000000      /* Freezer should not count it as freezeable */
 
 /*
  * Only the _current_ task can read/write to tsk->flags, but other