mm: always expand the stack with the mmap write lock held

This finishes the job of always holding the mmap write lock when
extending the user stack vma, and removes the 'write_locked' argument
from the vm helper functions again.

For some cases, we just avoid expanding the stack at all: drivers and
page pinning really shouldn't be extending any stacks.  Let's see if any
strange users really wanted that.

It's worth noting that architectures that weren't converted to the new
lock_mm_and_find_vma() helper function are left using the legacy
"expand_stack()" function, but it has been changed to drop the mmap_lock
and take it for writing while expanding the vma.  This makes it fairly
straightforward to convert the remaining architectures.

As a result of dropping and re-taking the lock, the calling conventions
for this function have also changed, since the old vma may no longer be
valid.  So it will now return the new vma if successful, and NULL - and
the lock dropped - if the area could not be extended.

Tested-by: Vegard Nossum <vegard.nossum@oracle.com>
Tested-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de> # ia64
Tested-by: Frank Scheiner <frank.scheiner@web.de> # ia64
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 11 deletions

diff --git a/mm/nommu.c b/mm/nommu.c
index f476c9ed36b3..37d0b03143f1 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -631,24 +631,20 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
 EXPORT_SYMBOL(find_vma);
 
 /*
- * find a VMA
- * - we don't extend stack VMAs under NOMMU conditions
- */
-struct vm_area_struct *find_extend_vma(struct mm_struct *mm, unsigned long addr)
-{
-	return find_vma(mm, addr);
-}
-
-/*
  * expand a stack to a given address
  * - not supported under NOMMU conditions
  */
-int expand_stack_locked(struct vm_area_struct *vma, unsigned long address,
-		bool write_locked)
+int expand_stack_locked(struct vm_area_struct *vma, unsigned long addr)
 {
 	return -ENOMEM;
 }
 
+struct vm_area_struct *expand_stack(struct mm_struct *mm, unsigned long addr)
+{
+	mmap_read_unlock(mm);
+	return NULL;
+}
+
 /*
  * look up the first VMA exactly that exactly matches addr
  * - should be called with mm->mmap_lock at least held readlocked