memcg: minor ->mm_owner fix/cleanups

Andrew,

You applied the last (4th) memcg-kill-config_mm_owner.patch, but other patches in this thread were ignored. Hopefully thi is because I sent them chaotically.

Let me resend 1-3 in case you missed them. Acked by Michal.

Oleg.

 init/main.c   |    1 -
 kernel/exit.c |   18 +++++++++++-------
 2 files changed, 11 insertions(+), 8 deletions(-)

"Search through everything else" in mm_update_next_owner() can hit a kthread which adopted this "mm" via use_mm(), it should not be used as mm->owner. Add the PF_KTHREAD check.

While at it, change this code to use for_each_process_thread() instead of deprecated do_each_thread/while_each_thread.

---
 kernel/exit.c |   10 ++++------
 1 files changed, 4 insertions(+), 6 deletions(-)

index ad7183a..e270d2a 100644
@@ -356,14 +356,12 @@ retry:
 	}
 
 	/*
-	 * Search through everything else. We should not get
-	 * here often
+	 * Search through everything else, we should not get here often.
 	 */
-	do_each_thread(g, c) {
-		if (c->mm == mm)
+	for_each_process_thread(g, c) {
+		if (!(c->flags & PF_KTHREAD) && c->mm == mm)
 			goto assign_new_owner;
-	} while_each_thread(g, c);
-
+	}
 	read_unlock(&tasklist_lock);
 	/*
 	 * We found no owner yet mm_users > 1: this implies that we are

1.5.5.1

for_each_process_thread() is sub-optimal. All threads share the same ->mm, we can swicth to the next process once we found a thread with ->mm != NULL and ->mm != mm.

---
 kernel/exit.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)

index e270d2a..429659c 100644
@@ -358,9 +358,15 @@ retry:
 	/*
 	 * Search through everything else, we should not get here often.
 	 */
-	for_each_process_thread(g, c) {
-		if (!(c->flags & PF_KTHREAD) && c->mm == mm)
-			goto assign_new_owner;
+	for_each_process(g) {
+		if (g->flags & PF_KTHREAD)
+			continue;
+		for_each_thread(g, c) {
+			if (c->mm == mm)
+				goto assign_new_owner;
+			if (c->mm)
+				break;
+		}
 	}
 	read_unlock(&tasklist_lock);
 	/*

1.5.5.1

Remove start_kernel()->mm_init_owner(&init_mm, &init_task).

This doesn't really hurt but unnecessary and misleading. init_task is the "swapper" thread == current, its ->mm is always NULL. And init_mm can only be used as ->active_mm, not as ->mm.

mm_init_owner() has a single caller with this patch, perhaps it should die. mm_init() can initialize ->owner under #ifdef.

---
 init/main.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

index 3815895..17090bb 100644
@@ -507,7 +507,6 @@ asmlinkage void __init start_kernel(void)
 	page_address_init();
 	pr_notice("%s", linux_banner);
 	setup_arch(&command_line);
-	mm_init_owner(&init_mm, &init_task);
 	mm_init_cpumask(&init_mm);
 	setup_command_line(command_line);
 	setup_nr_cpu_ids();

1.5.5.1

All of them are queued AFAICS. I do not know where those emails are archived so i've bounced them to you off-list.

Michal Hocko
SUSE Labs