report errors in /proc/*/*map* sanely

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/proc/base.c

@@ -225,15 +225,17 @@ static int check_mem_permission(struct task_struct *task)
 struct mm_struct *mm_for_maps(struct task_struct *task)
 {
 	struct mm_struct *mm;
+	int err;
 
-	if (mutex_lock_killable(&task->signal->cred_guard_mutex))
-		return NULL;
+	err =  mutex_lock_killable(&task->signal->cred_guard_mutex);
+	if (err)
+		return ERR_PTR(err);
 
 	mm = get_task_mm(task);
 	if (mm && mm != current->mm &&
 			!ptrace_may_access(task, PTRACE_MODE_READ)) {
 		mmput(mm);
-		mm = NULL;
+		mm = ERR_PTR(-EACCES);
 	}
 	mutex_unlock(&task->signal->cred_guard_mutex);
 

fs/proc/task_mmu.c

@@ -119,11 +119,11 @@ static void *m_start(struct seq_file *m, loff_t *pos)
 
 	priv->task = get_pid_task(priv->pid, PIDTYPE_PID);
 	if (!priv->task)
-		return NULL;
+		return ERR_PTR(-ESRCH);
 
 	mm = mm_for_maps(priv->task);
-	if (!mm)
-		return NULL;
+	if (!mm || IS_ERR(mm))
+		return mm;
 	down_read(&mm->mmap_sem);
 
 	tail_vma = get_gate_vma(priv->task);
@@ -728,9 +728,9 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
 	if (!task)
 		goto out;
 
-	ret = -EACCES;
 	mm = mm_for_maps(task);
-	if (!mm)
+	ret = PTR_ERR(mm);
+	if (!mm || IS_ERR(mm))
 		goto out_task;
 
 	ret = -EINVAL;

fs/proc/task_nommu.c

@@ -199,13 +199,13 @@ static void *m_start(struct seq_file *m, loff_t *pos)
 	/* pin the task and mm whilst we play with them */
 	priv->task = get_pid_task(priv->pid, PIDTYPE_PID);
 	if (!priv->task)
-		return NULL;
+		return ERR_PTR(-ESRCH);
 
 	mm = mm_for_maps(priv->task);
-	if (!mm) {
+	if (!mm || IS_ERR(mm)) {
 		put_task_struct(priv->task);
 		priv->task = NULL;
-		return NULL;
+		return mm;
 	}
 	down_read(&mm->mmap_sem);