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>

4 files changed, 39 insertions, 24 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 6f742f6658a9..81cfff82875b 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;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 899d7304d594..17e9a8e9a51d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -639,6 +639,8 @@ struct signal_struct {
         unsigned audit_tty;
         struct tty_audit_buf *tty_audit_buf;
 #endif
+
+        int oom_adj;    /* OOM kill score adjustment (bit shift) */
 };
 
 /* Context switch must be unlocked if interrupts are to be enabled */
@@ -1221,7 +1223,6 @@ struct task_struct {
          * a short time
          */
         unsigned char fpu_counter;
-        s8 oomkilladj; /* OOM kill score adjustment (bit shift). */
 #ifdef CONFIG_BLK_DEV_IO_TRACE
         unsigned int btrace_seq;
 #endif
diff --git a/kernel/fork.c b/kernel/fork.c
index 73a442b7be6d..1020977b57ca 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -880,6 +880,8 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
 
         tty_audit_fork(sig);
 
+        sig->oom_adj = current->signal->oom_adj;
+
         return 0;
 }
 
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index da4c342f2641..630b77fe862f 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -58,6 +58,10 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
         unsigned long points, cpu_time, run_time;
         struct mm_struct *mm;
         struct task_struct *child;
+        int oom_adj = p->signal->oom_adj;
+
+        if (oom_adj == OOM_DISABLE)
+                return 0;
 
         task_lock(p);
         mm = p->mm;
@@ -148,15 +152,15 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
                 points /= 8;
 
         /*
-         * Adjust the score by oomkilladj.
+         * Adjust the score by oom_adj.
          */
-        if (p->oomkilladj) {
-                if (p->oomkilladj > 0) {
+        if (oom_adj) {
+                if (oom_adj > 0) {
                         if (!points)
                                 points = 1;
-                        points <<= p->oomkilladj;
+                        points <<= oom_adj;
                 } else
-                        points >>= -(p->oomkilladj);
+                        points >>= -(oom_adj);
         }
 
 #ifdef DEBUG
@@ -251,7 +255,7 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
                         *ppoints = ULONG_MAX;
                 }
 
-                if (p->oomkilladj == OOM_DISABLE)
+                if (p->signal->oom_adj == OOM_DISABLE)
                         continue;
 
                 points = badness(p, uptime.tv_sec);
@@ -304,7 +308,7 @@ static void dump_tasks(const struct mem_cgroup *mem)
                 }
                 printk(KERN_INFO "[%5d] %5d %5d %8lu %8lu %3d     %3d %s\n",
                        p->pid, __task_cred(p)->uid, p->tgid, mm->total_vm,
-                       get_mm_rss(mm), (int)task_cpu(p), p->oomkilladj,
+                       get_mm_rss(mm), (int)task_cpu(p), p->signal->oom_adj,
                        p->comm);
                 task_unlock(p);
         } while_each_thread(g, p);
@@ -359,18 +363,9 @@ static int oom_kill_task(struct task_struct *p)
          * change to NULL at any time since we do not hold task_lock(p).
          * However, this is of no concern to us.
          */
-
-        if (mm == NULL)
+        if (!mm || p->signal->oom_adj == OOM_DISABLE)
                 return 1;
 
-        /*
-         * Don't kill the process if any threads are set to OOM_DISABLE
-         */
-        do_each_thread(g, q) {
-                if (q->mm == mm && q->oomkilladj == OOM_DISABLE)
-                        return 1;
-        } while_each_thread(g, q);
-
         __oom_kill_task(p, 1);
 
         /*
@@ -394,8 +389,9 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 
         if (printk_ratelimit()) {
                 printk(KERN_WARNING "%s invoked oom-killer: "
-                        "gfp_mask=0x%x, order=%d, oomkilladj=%d\n",
-                        current->comm, gfp_mask, order, current->oomkilladj);
+                        "gfp_mask=0x%x, order=%d, oom_adj=%d\n",
+                        current->comm, gfp_mask, order,
+                        current->signal->oom_adj);
                 task_lock(current);
                 cpuset_print_task_mems_allowed(current);
                 task_unlock(current);