oom: rewrite error handling for oom_adj and oom_score_adj tunables

It's better to use proper error handling in oom_adjust_write() and
oom_score_adj_write() instead of duplicating the locking order on various
exit paths.

Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Rientjes <rientjes@google.com>
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>

fs/proc/base.c

@@ -1023,36 +1023,39 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
 	memset(buffer, 0, sizeof(buffer));
 	if (count > sizeof(buffer) - 1)
 		count = sizeof(buffer) - 1;
-	if (copy_from_user(buffer, buf, count))
-		return -EFAULT;
+	if (copy_from_user(buffer, buf, count)) {
+		err = -EFAULT;
+		goto out;
+	}
 
 	err = strict_strtol(strstrip(buffer), 0, &oom_adjust);
 	if (err)
-		return -EINVAL;
+		goto out;
 	if ((oom_adjust < OOM_ADJUST_MIN || oom_adjust > OOM_ADJUST_MAX) &&
-	     oom_adjust != OOM_DISABLE)
-		return -EINVAL;
+	     oom_adjust != OOM_DISABLE) {
+		err = -EINVAL;
+		goto out;
+	}
 
 	task = get_proc_task(file->f_path.dentry->d_inode);
-	if (!task)
-		return -ESRCH;
+	if (!task) {
+		err = -ESRCH;
+		goto out;
+	}
 	if (!lock_task_sighand(task, &flags)) {
-		put_task_struct(task);
-		return -ESRCH;
+		err = -ESRCH;
+		goto err_task_struct;
 	}
 
 	if (oom_adjust < task->signal->oom_adj && !capable(CAP_SYS_RESOURCE)) {
-		unlock_task_sighand(task, &flags);
-		put_task_struct(task);
-		return -EACCES;
+		err = -EACCES;
+		goto err_sighand;
 	}
 
 	task_lock(task);
 	if (!task->mm) {
-		task_unlock(task);
-		unlock_task_sighand(task, &flags);
-		put_task_struct(task);
-		return -EINVAL;
+		err = -EINVAL;
+		goto err_task_lock;
 	}
 
 	if (oom_adjust != task->signal->oom_adj) {
@@ -1080,11 +1083,14 @@ 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:
 	put_task_struct(task);
-
-	return count;
+out:
+	return err < 0 ? err : count;
 }
 
 static const struct file_operations proc_oom_adjust_operations = {
@@ -1125,36 +1131,39 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
 	memset(buffer, 0, sizeof(buffer));
 	if (count > sizeof(buffer) - 1)
 		count = sizeof(buffer) - 1;
-	if (copy_from_user(buffer, buf, count))
-		return -EFAULT;
+	if (copy_from_user(buffer, buf, count)) {
+		err = -EFAULT;
+		goto out;
+	}
 
 	err = strict_strtol(strstrip(buffer), 0, &oom_score_adj);
 	if (err)
-		return -EINVAL;
+		goto out;
 	if (oom_score_adj < OOM_SCORE_ADJ_MIN ||
-			oom_score_adj > OOM_SCORE_ADJ_MAX)
-		return -EINVAL;
+			oom_score_adj > OOM_SCORE_ADJ_MAX) {
+		err = -EINVAL;
+		goto out;
+	}
 
 	task = get_proc_task(file->f_path.dentry->d_inode);
-	if (!task)
-		return -ESRCH;
+	if (!task) {
+		err = -ESRCH;
+		goto out;
+	}
 	if (!lock_task_sighand(task, &flags)) {
-		put_task_struct(task);
-		return -ESRCH;
+		err = -ESRCH;
+		goto err_task_struct;
 	}
 	if (oom_score_adj < task->signal->oom_score_adj &&
 			!capable(CAP_SYS_RESOURCE)) {
-		unlock_task_sighand(task, &flags);
-		put_task_struct(task);
-		return -EACCES;
+		err = -EACCES;
+		goto err_sighand;
 	}
 
 	task_lock(task);
 	if (!task->mm) {
-		task_unlock(task);
-		unlock_task_sighand(task, &flags);
-		put_task_struct(task);
-		return -EINVAL;
+		err = -EINVAL;
+		goto err_task_lock;
 	}
 	if (oom_score_adj != task->signal->oom_score_adj) {
 		if (oom_score_adj == OOM_SCORE_ADJ_MIN)
@@ -1172,10 +1181,14 @@ 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:
 	put_task_struct(task);
-	return count;
+out:
+	return err < 0 ? err : count;
 }
 
 static const struct file_operations proc_oom_score_adj_operations = {