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>

3 files changed, 37 insertions, 15 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 2e7addfd9803..318d8654989b 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -214,7 +214,7 @@ static void show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
         int flags = vma->vm_flags;
         unsigned long ino = 0;
         unsigned long long pgoff = 0;
-        unsigned long start;
+        unsigned long start, end;
         dev_t dev = 0;
         int len;
 
@@ -227,13 +227,15 @@ static void show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
 
         /* We don't show the stack guard page in /proc/maps */
         start = vma->vm_start;
-        if (vma->vm_flags & VM_GROWSDOWN)
-                if (!vma_stack_continue(vma->vm_prev, vma->vm_start))
-                        start += PAGE_SIZE;
+        if (stack_guard_page_start(vma, start))
+                start += PAGE_SIZE;
+        end = vma->vm_end;
+        if (stack_guard_page_end(vma, end))
+                end -= PAGE_SIZE;
 
         seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu %n",
                         start,
-                        vma->vm_end,
+                        end,
                         flags & VM_READ ? 'r' : '-',
                         flags & VM_WRITE ? 'w' : '-',
                         flags & VM_EXEC ? 'x' : '-',
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 2348db26bc3d..6507dde38b16 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1011,11 +1011,33 @@ int set_page_dirty_lock(struct page *page);
 int clear_page_dirty_for_io(struct page *page);
 
 /* Is the vma a continuation of the stack vma above it? */
-static inline int vma_stack_continue(struct vm_area_struct *vma, unsigned long addr)
+static inline int vma_growsdown(struct vm_area_struct *vma, unsigned long addr)
 {
         return vma && (vma->vm_end == addr) && (vma->vm_flags & VM_GROWSDOWN);
 }
 
+static inline int stack_guard_page_start(struct vm_area_struct *vma,
+                                             unsigned long addr)
+{
+        return (vma->vm_flags & VM_GROWSDOWN) &&
+                (vma->vm_start == addr) &&
+                !vma_growsdown(vma->vm_prev, addr);
+}
+
+/* Is the vma a continuation of the stack vma below it? */
+static inline int vma_growsup(struct vm_area_struct *vma, unsigned long addr)
+{
+        return vma && (vma->vm_start == addr) && (vma->vm_flags & VM_GROWSUP);
+}
+
+static inline int stack_guard_page_end(struct vm_area_struct *vma,
+                                           unsigned long addr)
+{
+        return (vma->vm_flags & VM_GROWSUP) &&
+                (vma->vm_end == addr) &&
+                !vma_growsup(vma->vm_next, addr);
+}
+
 extern unsigned long move_page_tables(struct vm_area_struct *vma,
                 unsigned long old_addr, struct vm_area_struct *new_vma,
                 unsigned long new_addr, unsigned long len);
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)