Re: [Suspend-devel] [PATCH -mm 1/2]: PM: Fix handling of stopped tasks

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Tuesday, 5 December 2006 22:26, Rafael J. Wysocki wrote:
> On Tuesday, 5 December 2006 22:03, Rafael J. Wysocki wrote:
> > Okay, I have replaced my [1/2] with the patch below ...
> > 
> > On Tuesday, 5 December 2006 11:34, Pavel Machek wrote:
<--snip-->
> 
> Well, now the task that was stopped before the suspend doesn't go to the
> refrigerator when it's received the continuation signal after the resume.
> Good, but is it sufficient?

Well, almost.

Namely, if you suspend with a stopped vi and you look at the dmesg output
after the resume, there will be something like this:

Restarting tasks ... <4> Strange, vi not stopped

which means that thaw_tasks() is confused by the lurking stopped task.  We can
fix that by checking if the task in question is not stopped before printing
the message in thaw_tasks() and we get this:

 kernel/power/process.c |   21 ++++++++++++++++++---
 kernel/signal.c        |    4 +++-
 2 files changed, 21 insertions(+), 4 deletions(-)

Index: linux-2.6.19-rc6-mm2/kernel/power/process.c
===================================================================
--- linux-2.6.19-rc6-mm2.orig/kernel/power/process.c	2006-12-05 21:10:00.000000000 +0100
+++ linux-2.6.19-rc6-mm2/kernel/power/process.c	2006-12-05 22:44:45.000000000 +0100
@@ -28,8 +28,7 @@ static inline int freezeable(struct task
 	if ((p == current) || 
 	    (p->flags & PF_NOFREEZE) ||
 	    (p->exit_state == EXIT_ZOMBIE) ||
-	    (p->exit_state == EXIT_DEAD) ||
-	    (p->state == TASK_STOPPED))
+	    (p->exit_state == EXIT_DEAD))
 		return 0;
 	return 1;
 }
@@ -103,6 +102,9 @@ static unsigned int try_to_freeze_tasks(
 			if (frozen(p))
 				continue;
 
+			if (p->state == TASK_STOPPED && freezing(p))
+				continue;
+
 			if (p->state == TASK_TRACED &&
 			    (frozen(p->parent) ||
 			     p->parent->state == TASK_STOPPED)) {
@@ -185,6 +187,18 @@ int freeze_processes(void)
 	return 0;
 }
 
+static inline void release_stopped_tasks(void)
+{
+	struct task_struct *g, *p;
+
+	read_lock(&tasklist_lock);
+	do_each_thread(g, p) {
+		if (p->state == TASK_STOPPED && freezing(p))
+			cancel_freezing(p);
+	} while_each_thread(g, p);
+	read_unlock(&tasklist_lock);
+}
+
 static void thaw_tasks(int thaw_user_space)
 {
 	struct task_struct *g, *p;
@@ -197,7 +211,7 @@ static void thaw_tasks(int thaw_user_spa
 		if (is_user_space(p) == !thaw_user_space)
 			continue;
 
-		if (!thaw_process(p))
+		if (!thaw_process(p) && p->state != TASK_STOPPED)
 			printk(KERN_WARNING " Strange, %s not stopped\n",
 				p->comm );
 	} while_each_thread(g, p);
@@ -207,6 +221,7 @@ static void thaw_tasks(int thaw_user_spa
 void thaw_processes(void)
 {
 	printk("Restarting tasks ... ");
+	release_stopped_tasks();
 	thaw_tasks(FREEZER_KERNEL_THREADS);
 	thaw_tasks(FREEZER_USER_SPACE);
 	schedule();
Index: linux-2.6.19-rc6-mm2/kernel/signal.c
===================================================================
--- linux-2.6.19-rc6-mm2.orig/kernel/signal.c	2006-12-05 21:10:00.000000000 +0100
+++ linux-2.6.19-rc6-mm2/kernel/signal.c	2006-12-05 21:11:31.000000000 +0100
@@ -1829,7 +1829,9 @@ finish_stop(int stop_count)
 		read_unlock(&tasklist_lock);
 	}
 
-	schedule();
+	do {
+		schedule();
+	} while (try_to_freeze());
 	/*
 	 * Now we don't run again until continued.
 	 */

But now it looks almost like my [1/2], doesn't it? ;-)

Greetings,
Rafael


-- 
If you don't have the time to read,
you don't have the time or the tools to write.
		- Stephen King