oom: move oom_adj value from task_struct to signal_struct

Currently, OOM logic callflow is here.

    __out_of_memory()
        select_bad_process()            for each task
            badness()                   calculate badness of one task
                oom_kill_process()      search child
                    oom_kill_task()     kill target task and mm shared tasks with it

example, process-A have two thread, thread-A and thread-B and it have very
fat memory and each thread have following oom_adj and oom_score.

     thread-A: oom_adj = OOM_DISABLE, oom_score = 0
     thread-B: oom_adj = 0,           oom_score = very-high

Then, select_bad_process() select thread-B, but oom_kill_task() refuse
kill the task because thread-A have OOM_DISABLE.  Thus __out_of_memory()
call select_bad_process() again.  but select_bad_process() select the same
task.  It mean kernel fall in livelock.

The fact is, select_bad_process() must select killable task.  otherwise
OOM logic go into livelock.

And root cause is, oom_adj shouldn't be per-thread value.  it should be
per-process value because OOM-killer kill a process, not thread.  Thus
This patch moves oomkilladj (now more appropriately named oom_adj) from
struct task_struct to struct signal_struct.  it naturally prevent
select_bad_process() choose wrong task.

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: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 20 insertions, 4 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 6f742f6658a..81cfff82875 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -999,11 +999,17 @@ static ssize_t oom_adjust_read(struct file *file, char __user *buf,
 	struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
 	char buffer[PROC_NUMBUF];
 	size_t len;
-	int oom_adjust;
+	int oom_adjust = OOM_DISABLE;
+	unsigned long flags;
 
 	if (!task)
 		return -ESRCH;
-	oom_adjust = task->oomkilladj;
+
+	if (lock_task_sighand(task, &flags)) {
+		oom_adjust = task->signal->oom_adj;
+		unlock_task_sighand(task, &flags);
+	}
+
 	put_task_struct(task);
 
 	len = snprintf(buffer, sizeof(buffer), "%i\n", oom_adjust);
@@ -1017,6 +1023,7 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
 	struct task_struct *task;
 	char buffer[PROC_NUMBUF], *end;
 	int oom_adjust;
+	unsigned long flags;
 
 	memset(buffer, 0, sizeof(buffer));
 	if (count > sizeof(buffer) - 1)
@@ -1032,11 +1039,20 @@ 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;
-	if (oom_adjust < task->oomkilladj && !capable(CAP_SYS_RESOURCE)) {
+	if (!lock_task_sighand(task, &flags)) {
+		put_task_struct(task);
+		return -ESRCH;
+	}
+
+	if (oom_adjust < task->signal->oom_adj && !capable(CAP_SYS_RESOURCE)) {
+		unlock_task_sighand(task, &flags);
 		put_task_struct(task);
 		return -EACCES;
 	}
-	task->oomkilladj = oom_adjust;
+
+	task->signal->oom_adj = oom_adjust;
+
+	unlock_task_sighand(task, &flags);
 	put_task_struct(task);
 	if (end - buffer == 0)
 		return -EIO;