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, 9 insertions, 20 deletions

diff --git a/kernel/power/process.c b/kernel/power/process.c
index 02e490e..eefca85 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -120,22 +120,12 @@ static unsigned int try_to_freeze_tasks(int freeze_user_space)
 				cancel_freezing(p);
 				continue;
 			}
-			if (is_user_space(p)) {
-				if (!freeze_user_space)
-					continue;
-
-				/* Freeze the task unless there is a vfork
-				 * completion pending
-				 */
-				if (!p->vfork_done)
-					freeze_process(p);
-			} else {
-				if (freeze_user_space)
-					continue;
-
-				freeze_process(p);
-			}
-			todo++;
+			if (is_user_space(p) == !freeze_user_space)
+				continue;
+
+			freeze_process(p);
+			if (!freezer_should_skip(p))
+				todo++;
 		} while_each_thread(g, p);
 		read_unlock(&tasklist_lock);
 		yield();			/* Yield is okay here */
@@ -161,7 +151,8 @@ static unsigned int try_to_freeze_tasks(int freeze_user_space)
 				continue;
 
 			task_lock(p);
-			if (freezeable(p) && !frozen(p))
+			if (freezeable(p) && !frozen(p) &&
+			    !freezer_should_skip(p))
 				printk(KERN_ERR " %s\n", p->comm);
 
 			cancel_freezing(p);
@@ -210,9 +201,7 @@ static void thaw_tasks(int thaw_user_space)
 		if (is_user_space(p) == !thaw_user_space)
 			continue;
 
-		if (!thaw_process(p))
-			printk(KERN_WARNING " Strange, %s not stopped\n",
-				p->comm );
+		thaw_process(p);
 	} while_each_thread(g, p);
 	read_unlock(&tasklist_lock);
 }