[PATCH] proc: add missing 'mm' variable in nommu is_stack()

[Arnd Bergmann]

A recent revert left an incomplete function in fs/proc/task_nommu.c,
causing a build error for any NOMMU configuration with procfs:

fs/proc/task_nommu.c:132:28: error: 'mm' undeclared (first use in this function)
   stack = vma->vm_start <= mm->start_stack &&

Evidently, there is just a missing variable that is available
in the calling function but not inside of is_stack(). This
adds it.

Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Fixes: e87d4fd02f40 ("proc: revert /proc/<pid>/maps [stack:TID] annotation")
---
This came up today on my ARM randconfig builds with linux-next.
I did not run the kernel to see if the code actually works, but
it seems straightforward enough.

diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
index 60ab72e38f78..faacb0c0d857 100644
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -126,6 +126,7 @@ unsigned long task_statm(struct mm_struct *mm,
 static int is_stack(struct proc_maps_private *priv,
 		    struct vm_area_struct *vma, int is_pid)
 {
+	struct mm_struct *mm = vma->vm_mm;
 	int stack = 0;
 
 	if (is_pid) {