Don't lock guardpage if the stack is growing up

Linux kernel excludes guard page when performing mlock on a VMA with
down-growing stack. However, some architectures have up-growing stack
and locking the guard page should be excluded in this case too.

This patch fixes lvm2 on PA-RISC (and possibly other architectures with
up-growing stack). lvm2 calculates number of used pages when locking and
when unlocking and reports an internal error if the numbers mismatch.

[ Patch changed fairly extensively to also fix /proc/<pid>/maps for the
  grows-up case, and to move things around a bit to clean it all up and
  share the infrstructure with the /proc bits.

  Tested on ia64 that has both grow-up and grow-down segments  - Linus ]

Signed-off-by: Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz>
Tested-by: Tony Luck <tony.luck@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 9 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 27f425378112..61e66f026563 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1412,9 +1412,8 @@ no_page_table:
 
 static inline int stack_guard_page(struct vm_area_struct *vma, unsigned long addr)
 {
-        return (vma->vm_flags & VM_GROWSDOWN) &&
-                (vma->vm_start == addr) &&
-                !vma_stack_continue(vma->vm_prev, addr);
+        return stack_guard_page_start(vma, addr) ||
+               stack_guard_page_end(vma, addr+PAGE_SIZE);
 }
 
 /**
@@ -1551,12 +1550,6 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                         continue;
                 }
 
-                /*
-                 * For mlock, just skip the stack guard page.
-                 */
-                if ((gup_flags & FOLL_MLOCK) && stack_guard_page(vma, start))
-                        goto next_page;
-
                 do {
                         struct page *page;
                         unsigned int foll_flags = gup_flags;
@@ -1573,6 +1566,11 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                                 int ret;
                                 unsigned int fault_flags = 0;
 
+                                /* For mlock, just skip the stack guard page. */
+                                if (foll_flags & FOLL_MLOCK) {
+                                        if (stack_guard_page(vma, start))
+                                                goto next_page;
+                                }
                                 if (foll_flags & FOLL_WRITE)
                                         fault_flags |= FAULT_FLAG_WRITE;
                                 if (nonblocking)