[patch 2/3 v3] oom: avoid killing a task if a thread sharing its mm cannot be killed

[David Rientjes <rientjes@google.com>]

The oom killer's goal is to kill a memory-hogging task so that it may
exit, free its memory, and allow the current context to allocate the
memory that triggered it in the first place.  Thus, killing a task is
pointless if other threads sharing its mm cannot be killed because of its
/proc/pid/oom_adj or /proc/pid/oom_score_adj value.

This patch checks whether any other thread sharing p->mm has an
oom_score_adj of OOM_SCORE_ADJ_MIN.  If so, the thread cannot be killed
and oom_badness(p) returns 0, meaning it's unkillable.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/oom_kill.c |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -162,10 +162,11 @@ unsigned int oom_badness(struct task_struct *p, struct mem_cgroup *mem,
 		return 0;
 
 	/*
-	 * Shortcut check for OOM_SCORE_ADJ_MIN so the entire heuristic doesn't
-	 * need to be executed for something that cannot be killed.
+	 * Shortcut check for a thread sharing p->mm that is OOM_SCORE_ADJ_MIN
+	 * so the entire heuristic doesn't need to be executed for something
+	 * that cannot be killed.
 	 */
-	if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
+	if (atomic_read(&p->mm->oom_disable_count)) {
 		task_unlock(p);
 		return 0;
 	}
@@ -675,7 +676,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
 	read_lock(&tasklist_lock);
 	if (sysctl_oom_kill_allocating_task &&
 	    !oom_unkillable_task(current, NULL, nodemask) &&
-	    (current->signal->oom_adj != OOM_DISABLE)) {
+	    current->mm && !atomic_read(&current->mm->oom_disable_count)) {
 		/*
 		 * oom_kill_process() needs tasklist_lock held.  If it returns
 		 * non-zero, current could not be killed so we must fallback to

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