oom: remove oom_disable_count

This removes mm->oom_disable_count entirely since it's unnecessary and
currently buggy.  The counter was intended to be per-process but it's
currently decremented in the exit path for each thread that exits, causing
it to underflow.

The count was originally intended to prevent oom killing threads that
share memory with threads that cannot be killed since it doesn't lead to
future memory freeing.  The counter could be fixed to represent all
threads sharing the same mm, but it's better to remove the count since:

 - it is possible that the OOM_DISABLE thread sharing memory with the
   victim is waiting on that thread to exit and will actually cause
   future memory freeing, and

 - there is no guarantee that a thread is disabled from oom killing just
   because another thread sharing its mm is oom disabled.

Signed-off-by: David Rientjes <rientjes@google.com>
Reported-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Ying Han <yinghan@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 1 insertions, 11 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 2913b3509d42..d0b7d988f873 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -681,8 +681,6 @@ static void exit_mm(struct task_struct * tsk)
         enter_lazy_tlb(mm, current);
         /* We don't want this task to be frozen prematurely */
         clear_freeze_flag(tsk);
-        if (tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
-                atomic_dec(&mm->oom_disable_count);
         task_unlock(tsk);
         mm_update_next_owner(mm);
         mmput(mm);
diff --git a/kernel/fork.c b/kernel/fork.c
index 8e6b6f4fb272..70d76191afb9 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -501,7 +501,6 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
         mm->cached_hole_size = ~0UL;
         mm_init_aio(mm);
         mm_init_owner(mm, p);
-        atomic_set(&mm->oom_disable_count, 0);
 
         if (likely(!mm_alloc_pgd(mm))) {
                 mm->def_flags = 0;
@@ -816,8 +815,6 @@ good_mm:
         /* Initializing for Swap token stuff */
         mm->token_priority = 0;
         mm->last_interval = 0;
-        if (tsk->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
-                atomic_inc(&mm->oom_disable_count);
 
         tsk->mm = mm;
         tsk->active_mm = mm;
@@ -1391,13 +1388,8 @@ bad_fork_cleanup_io:
 bad_fork_cleanup_namespaces:
         exit_task_namespaces(p);
 bad_fork_cleanup_mm:
-        if (p->mm) {
-                task_lock(p);
-                if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
-                        atomic_dec(&p->mm->oom_disable_count);
-                task_unlock(p);
+        if (p->mm)
                 mmput(p->mm);
-        }
 bad_fork_cleanup_signal:
         if (!(clone_flags & CLONE_THREAD))
                 free_signal_struct(p->signal);