oom: fix locking for oom_adj and oom_score_adj

The locking order in oom_adjust_write() and oom_score_adj_write() for
task->alloc_lock and task->sighand->siglock is reversed, and lockdep
notices that irqs could encounter an ABBA scenario.

This fixes the locking order so that we always take task_lock(task) prior
to lock_task_sighand(task).

Signed-off-by: David Rientjes <rientjes@google.com>
Reported-by: Andrew Morton <akpm@linux-foundation.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Ying Han <yinghan@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 21 insertions, 19 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 34d11ac31f2e..53dc8ad40ae6 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1042,9 +1042,16 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
                 err = -ESRCH;
                 goto out;
         }
+
+        task_lock(task);
+        if (!task->mm) {
+                err = -EINVAL;
+                goto err_task_lock;
+        }
+
         if (!lock_task_sighand(task, &flags)) {
                 err = -ESRCH;
-                goto err_task_struct;
+                goto err_task_lock;
         }
 
         if (oom_adjust < task->signal->oom_adj && !capable(CAP_SYS_RESOURCE)) {
@@ -1052,12 +1059,6 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
                 goto err_sighand;
         }
 
-        task_lock(task);
-        if (!task->mm) {
-                err = -EINVAL;
-                goto err_task_lock;
-        }
-
         if (oom_adjust != task->signal->oom_adj) {
                 if (oom_adjust == OOM_DISABLE)
                         atomic_inc(&task->mm->oom_disable_count);
@@ -1083,11 +1084,10 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
         else
                 task->signal->oom_score_adj = (oom_adjust * OOM_SCORE_ADJ_MAX) /
                                                                 -OOM_DISABLE;
-err_task_lock:
-        task_unlock(task);
 err_sighand:
         unlock_task_sighand(task, &flags);
-err_task_struct:
+err_task_lock:
+        task_unlock(task);
         put_task_struct(task);
 out:
         return err < 0 ? err : count;
@@ -1150,21 +1150,24 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
                 err = -ESRCH;
                 goto out;
         }
+
+        task_lock(task);
+        if (!task->mm) {
+                err = -EINVAL;
+                goto err_task_lock;
+        }
+
         if (!lock_task_sighand(task, &flags)) {
                 err = -ESRCH;
-                goto err_task_struct;
+                goto err_task_lock;
         }
+
         if (oom_score_adj < task->signal->oom_score_adj &&
                         !capable(CAP_SYS_RESOURCE)) {
                 err = -EACCES;
                 goto err_sighand;
         }
 
-        task_lock(task);
-        if (!task->mm) {
-                err = -EINVAL;
-                goto err_task_lock;
-        }
         if (oom_score_adj != task->signal->oom_score_adj) {
                 if (oom_score_adj == OOM_SCORE_ADJ_MIN)
                         atomic_inc(&task->mm->oom_disable_count);
@@ -1181,11 +1184,10 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
         else
                 task->signal->oom_adj = (oom_score_adj * OOM_ADJUST_MAX) /
                                                         OOM_SCORE_ADJ_MAX;
-err_task_lock:
-        task_unlock(task);
 err_sighand:
         unlock_task_sighand(task, &flags);
-err_task_struct:
+err_task_lock:
+        task_unlock(task);
         put_task_struct(task);
 out:
         return err < 0 ? err : count;