[patch -mm 4/6] oom: introduce find_lock_task_mm to fix mm false positives fix

[David Rientjes <rientjes@google.com>]

find_lock_task_mm() should be documented so that we clearly understand
what it does and why we need it.

At the same time, remove a stale coment about dereferencing of a local
variable "mm" in badness() which no longer exists and was removed when
find_lock_task_mm() was added.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/oom_kill.c |   10 ++++++----
 1 files changed, 6 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
@@ -81,6 +81,12 @@ static bool has_intersects_mems_allowed(struct task_struct *tsk,
 }
 #endif /* CONFIG_NUMA */
 
+/*
+ * The process p may have detached its own ->mm while exiting or through
+ * use_mm(), but one or more of its subthreads may still have a valid
+ * pointer.  Return p, or any of its subthreads with a valid ->mm, with
+ * task_lock() held.
+ */
 static struct task_struct *find_lock_task_mm(struct task_struct *p)
 {
 	struct task_struct *t = p;
@@ -135,10 +141,6 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
 	 * The memory size of the process is the basis for the badness.
 	 */
 	points = p->mm->total_vm;
-
-	/*
-	 * After this unlock we can no longer dereference local variable `mm'
-	 */
 	task_unlock(p);
 
 	/*

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