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, 6 insertions, 30 deletions

diff --git a/arch/ia64/mm/fault.c b/arch/ia64/mm/fault.c
index 85c4d9ac8686..5458b52b4009 100644
--- a/arch/ia64/mm/fault.c
+++ b/arch/ia64/mm/fault.c
@@ -110,10 +110,12 @@ retry:
          * register backing store that needs to expand upwards, in
          * this case vma will be null, but prev_vma will ne non-null
          */
-        if (( !vma && prev_vma ) || (address < vma->vm_start) )
-		goto check_expansion;
+        if (( !vma && prev_vma ) || (address < vma->vm_start) ) {
+		vma = expand_stack(mm, address);
+		if (!vma)
+			goto bad_area_nosemaphore;
+	}
 
-  good_area:
 	code = SEGV_ACCERR;
 
 	/* OK, we've got a good vm_area for this memory area.  Check the access permissions: */
@@ -177,35 +179,9 @@ retry:
 	mmap_read_unlock(mm);
 	return;
 
-  check_expansion:
-	if (!(prev_vma && (prev_vma->vm_flags & VM_GROWSUP) && (address == prev_vma->vm_end))) {
-		if (!vma)
-			goto bad_area;
-		if (!(vma->vm_flags & VM_GROWSDOWN))
-			goto bad_area;
-		if (REGION_NUMBER(address) != REGION_NUMBER(vma->vm_start)
-		    || REGION_OFFSET(address) >= RGN_MAP_LIMIT)
-			goto bad_area;
-		if (expand_stack(vma, address))
-			goto bad_area;
-	} else {
-		vma = prev_vma;
-		if (REGION_NUMBER(address) != REGION_NUMBER(vma->vm_start)
-		    || REGION_OFFSET(address) >= RGN_MAP_LIMIT)
-			goto bad_area;
-		/*
-		 * Since the register backing store is accessed sequentially,
-		 * we disallow growing it by more than a page at a time.
-		 */
-		if (address > vma->vm_end + PAGE_SIZE - sizeof(long))
-			goto bad_area;
-		if (expand_upwards(vma, address))
-			goto bad_area;
-	}
-	goto good_area;
-
   bad_area:
 	mmap_read_unlock(mm);
+  bad_area_nosemaphore:
 	if ((isr & IA64_ISR_SP)
 	    || ((isr & IA64_ISR_NA) && (isr & IA64_ISR_CODE_MASK) == IA64_ISR_CODE_LFETCH))
 	{