[PATCH 3/5] oom: Fix child process iteration properly

[KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>]

Oleg pointed out that current oom child process iterating logic is wrong.

  > list_for_each_entry(p->children) can only see the tasks forked
  > by p, it can't see other children forked by its sub-threads.

This patch fixes it.

Reported-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
---
 mm/oom_kill.c |   34 ++++++++++++++++++++--------------
 1 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 70e1a85..1bdf27d 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -88,6 +88,7 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
 {
 	unsigned long points, cpu_time, run_time;
 	struct task_struct *c;
+	struct task_struct *t = p;
 	struct task_struct *child;
 	int oom_adj = p->signal->oom_adj;
 	struct task_cputime task_time;
@@ -125,14 +126,16 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
 	 * child is eating the vast majority of memory, adding only half
 	 * to the parents will make the child our kill candidate of choice.
 	 */
-	list_for_each_entry(c, &p->children, sibling) {
-		child = find_lock_task_mm(c);
-		if (child) {
-			if (child->mm != p->mm)
-				points += child->mm->total_vm/2 + 1;
-			task_unlock(child);
+	do {
+		list_for_each_entry(c, &t->children, sibling) {
+			child = find_lock_task_mm(c);
+			if (child) {
+				if (child->mm != p->mm)
+					points += child->mm->total_vm/2 + 1;
+				task_unlock(child);
+			}
 		}
-	}
+	} while_each_thread(p, t);
 
 	/*
 	 * CPU time is in tens of seconds and run time is in thousands
@@ -432,6 +435,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 			    const char *message)
 {
 	struct task_struct *c;
+	struct task_struct *t = p;
 
 	if (printk_ratelimit())
 		dump_header(p, gfp_mask, order, mem);
@@ -449,14 +453,16 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 					message, task_pid_nr(p), p->comm, points);
 
 	/* Try to kill a child first */
-	list_for_each_entry(c, &p->children, sibling) {
-		if (c->mm == p->mm)
-			continue;
+	do {
+		list_for_each_entry(c, &t->children, sibling) {
+			if (c->mm == p->mm)
+				continue;
 
-		/* Ok, Kill the child */
-		if (!__oom_kill_process(c, mem, 1))
-			return 0;
-	}
+			/* Ok, Kill the child */
+			if (!__oom_kill_process(c, mem, 1))
+				return 0;
+		}
+	} while_each_thread(p, t);
 
 	return __oom_kill_process(p, mem, 1);
 }
-- 
1.6.5.2



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