mm: revert "oom: move oom_adj value"

The commit 2ff05b2b (oom: move oom_adj value) moveed the oom_adj value to
the mm_struct.  It was a very good first step for sanitize OOM.

However Paul Menage reported the commit makes regression to his job
scheduler.  Current OOM logic can kill OOM_DISABLED process.

Why? His program has the code of similar to the following.

	...
	set_oom_adj(OOM_DISABLE); /* The job scheduler never killed by oom */
	...
	if (vfork() == 0) {
		set_oom_adj(0); /* Invoked child can be killed */
		execve("foo-bar-cmd");
	}
	....

vfork() parent and child are shared the same mm_struct.  then above
set_oom_adj(0) doesn't only change oom_adj for vfork() child, it's also
change oom_adj for vfork() parent.  Then, vfork() parent (job scheduler)
lost OOM immune and it was killed.

Actually, fork-setting-exec idiom is very frequently used in userland program.
We must not break this assumption.

Then, this patch revert commit 2ff05b2b and related commit.

Reverted commit list
---------------------
- commit 2ff05b2b4e (oom: move oom_adj value from task_struct to mm_struct)
- commit 4d8b9135c3 (oom: avoid unnecessary mm locking and scanning for OOM_DISABLE)
- commit 8123681022 (oom: only oom kill exiting tasks with attached memory)
- commit 933b787b57 (mm: copy over oom_adj value at fork time)

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 16 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 175db25..6f742f6 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1003,12 +1003,7 @@ static ssize_t oom_adjust_read(struct file *file, char __user *buf,
 
 	if (!task)
 		return -ESRCH;
-	task_lock(task);
-	if (task->mm)
-		oom_adjust = task->mm->oom_adj;
-	else
-		oom_adjust = OOM_DISABLE;
-	task_unlock(task);
+	oom_adjust = task->oomkilladj;
 	put_task_struct(task);
 
 	len = snprintf(buffer, sizeof(buffer), "%i\n", oom_adjust);
@@ -1037,19 +1032,11 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
 	task = get_proc_task(file->f_path.dentry->d_inode);
 	if (!task)
 		return -ESRCH;
-	task_lock(task);
-	if (!task->mm) {
-		task_unlock(task);
-		put_task_struct(task);
-		return -EINVAL;
-	}
-	if (oom_adjust < task->mm->oom_adj && !capable(CAP_SYS_RESOURCE)) {
-		task_unlock(task);
+	if (oom_adjust < task->oomkilladj && !capable(CAP_SYS_RESOURCE)) {
 		put_task_struct(task);
 		return -EACCES;
 	}
-	task->mm->oom_adj = oom_adjust;
-	task_unlock(task);
+	task->oomkilladj = oom_adjust;
 	put_task_struct(task);
 	if (end - buffer == 0)
 		return -EIO;