[PATCH] TASK_SIZE is variable.

Bad things can happen if a 32-bit process is the last user of a 64-bit mm. 
TASK_SIZE isn't a constant, and we can end up clearing page tables only up
to the 32-bit TASK_SIZE instead of all the way.  We should probably
double-check every instance of TASK_SIZE or USER_PTRS_PER_PGD for this kind
of problem.

We should also double-check that MM_VM_SIZE() and other such things are
correctly defined on all architectures.  I already fixed ppc64 which let it
stay as TASK_SIZE, and hence dependent on the _current_ context instead of
the mm in the argument.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/mmap.c

@@ -1612,8 +1612,8 @@ static void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *prev,
 	unsigned long last = end + PGDIR_SIZE - 1;
 	struct mm_struct *mm = tlb->mm;
 
-	if (last > TASK_SIZE || last < end)
-		last = TASK_SIZE;
+	if (last > MM_VM_SIZE(mm) || last < end)
+		last = MM_VM_SIZE(mm);
 
 	if (!prev) {
 		prev = mm->mmap;