1 files changed, 30 insertions, 11 deletions

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index c0c97aea837f..a3a32ae02e9d 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -336,7 +336,7 @@ enum oom_scan_t oom_scan_process_thread(struct task_struct *task,
 
 /*
  * Simple selection loop. We chose the process with the highest
- * number of 'points'. We expect the caller will lock the tasklist.
+ * number of 'points'.
  *
  * (not docbooked, we don't want this one cluttering up the manual)
  */
@@ -348,6 +348,7 @@ static struct task_struct *select_bad_process(unsigned int *ppoints,
         struct task_struct *chosen = NULL;
         unsigned long chosen_points = 0;
 
+        rcu_read_lock();
         do_each_thread(g, p) {
                 unsigned int points;
 
@@ -360,6 +361,7 @@ static struct task_struct *select_bad_process(unsigned int *ppoints,
                 case OOM_SCAN_CONTINUE:
                         continue;
                 case OOM_SCAN_ABORT:
+                        rcu_read_unlock();
                         return ERR_PTR(-1UL);
                 case OOM_SCAN_OK:
                         break;
@@ -370,6 +372,9 @@ static struct task_struct *select_bad_process(unsigned int *ppoints,
                         chosen_points = points;
                 }
         } while_each_thread(g, p);
+        if (chosen)
+                get_task_struct(chosen);
+        rcu_read_unlock();
 
         *ppoints = chosen_points * 1000 / totalpages;
         return chosen;
@@ -385,8 +390,6 @@ static struct task_struct *select_bad_process(unsigned int *ppoints,
  * are not shown.
  * State information includes task's pid, uid, tgid, vm size, rss, nr_ptes,
  * swapents, oom_score_adj value, and name.
- *
- * Call with tasklist_lock read-locked.
  */
 static void dump_tasks(const struct mem_cgroup *memcg, const nodemask_t *nodemask)
 {
@@ -394,6 +397,7 @@ static void dump_tasks(const struct mem_cgroup *memcg, const nodemask_t *nodemas
         struct task_struct *task;
 
         pr_info("[ pid ]   uid  tgid total_vm      rss nr_ptes swapents oom_score_adj name\n");
+        rcu_read_lock();
         for_each_process(p) {
                 if (oom_unkillable_task(p, memcg, nodemask))
                         continue;
@@ -416,6 +420,7 @@ static void dump_tasks(const struct mem_cgroup *memcg, const nodemask_t *nodemas
                         task->signal->oom_score_adj, task->comm);
                 task_unlock(task);
         }
+        rcu_read_unlock();
 }
 
 static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
@@ -436,6 +441,10 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
 }
 
 #define K(x) ((x) << (PAGE_SHIFT-10))
+/*
+ * Must be called while holding a reference to p, which will be released upon
+ * returning.
+ */
 void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
                       unsigned int points, unsigned long totalpages,
                       struct mem_cgroup *memcg, nodemask_t *nodemask,
@@ -455,6 +464,7 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
          */
         if (p->flags & PF_EXITING) {
                 set_tsk_thread_flag(p, TIF_MEMDIE);
+                put_task_struct(p);
                 return;
         }
 
@@ -472,6 +482,7 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
          * parent.  This attempts to lose the minimal amount of work done while
          * still freeing memory.
          */
+        read_lock(&tasklist_lock);
         do {
                 list_for_each_entry(child, &t->children, sibling) {
                         unsigned int child_points;
@@ -484,15 +495,26 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
                         child_points = oom_badness(child, memcg, nodemask,
                                                                 totalpages);
                         if (child_points > victim_points) {
+                                put_task_struct(victim);
                                 victim = child;
                                 victim_points = child_points;
+                                get_task_struct(victim);
                         }
                 }
         } while_each_thread(p, t);
+        read_unlock(&tasklist_lock);
 
-        victim = find_lock_task_mm(victim);
-        if (!victim)
+        rcu_read_lock();
+        p = find_lock_task_mm(victim);
+        if (!p) {
+                rcu_read_unlock();
+                put_task_struct(victim);
                 return;
+        } else if (victim != p) {
+                get_task_struct(p);
+                put_task_struct(victim);
+                victim = p;
+        }
 
         /* mm cannot safely be dereferenced after task_unlock(victim) */
         mm = victim->mm;
@@ -523,9 +545,11 @@ void oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
                         task_unlock(p);
                         do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
                 }
+        rcu_read_unlock();
 
         set_tsk_thread_flag(victim, TIF_MEMDIE);
         do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
+        put_task_struct(victim);
 }
 #undef K
 
@@ -546,9 +570,7 @@ static void check_panic_on_oom(enum oom_constraint constraint, gfp_t gfp_mask,
                 if (constraint != CONSTRAINT_NONE)
                         return;
         }
-        read_lock(&tasklist_lock);
         dump_header(NULL, gfp_mask, order, NULL, nodemask);
-        read_unlock(&tasklist_lock);
         panic("Out of memory: %s panic_on_oom is enabled\n",
                 sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
 }
@@ -721,10 +743,10 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
         mpol_mask = (constraint == CONSTRAINT_MEMORY_POLICY) ? nodemask : NULL;
         check_panic_on_oom(constraint, gfp_mask, order, mpol_mask);
 
-        read_lock(&tasklist_lock);
         if (sysctl_oom_kill_allocating_task && current->mm &&
             !oom_unkillable_task(current, NULL, nodemask) &&
             current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
+                get_task_struct(current);
                 oom_kill_process(current, gfp_mask, order, 0, totalpages, NULL,
                                  nodemask,
                                  "Out of memory (oom_kill_allocating_task)");
@@ -735,7 +757,6 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
         /* Found nothing?!?! Either we hang forever, or we panic. */
         if (!p) {
                 dump_header(NULL, gfp_mask, order, NULL, mpol_mask);
-                read_unlock(&tasklist_lock);
                 panic("Out of memory and no killable processes...\n");
         }
         if (PTR_ERR(p) != -1UL) {
@@ -744,8 +765,6 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
                 killed = 1;
         }
 out:
-        read_unlock(&tasklist_lock);
-
         /*
          * Give the killed threads a good chance of exiting before trying to
          * allocate memory again.