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mm: revert "oom: move oom_adj value"

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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 <[email protected]>
Cc: Paul Menage <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Mel Gorman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
KOSAKI Motohiro 2009-08-18 14:11:10 -07:00 • committed by Linus Torvalds
commit 0753ba01e1
6 changed files with 48 additions and 54 deletions
Download patch file Download diff file Expand all files Collapse all files

19
fs/proc/base.c
View file

@ -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;