From: Oleg Nesterov <oleg@tv-sign.ru>
Hugetlbfs mmap with MAP_PRIVATE becomes MAP_SHARED silently, but
vma->vm_flags have no VM_SHARED bit. Reading from /dev/zero into hugetlb
area will do:
read_zero()
read_zero_pagealigned()
if (vma->vm_flags & VM_SHARED)
break; // fallback to clear_user()
zap_page_range();
zeromap_page_range();
It will hit BUG_ON() in unmap_hugepage_range() if region is not huge page
aligned, or silently convert it into the private anonymous mapping.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-sparc64-akpm/drivers/char/mem.c | 2 +-
1 files changed, 1 insertion(+), 1 deletion(-)
diff -puN drivers/char/mem.c~dev-zero-vs-hugetlb-mappings drivers/char/mem.c
--- 25-sparc64/drivers/char/mem.c~dev-zero-vs-hugetlb-mappings 2004-07-31 20:57:35.137918184 -0700
+++ 25-sparc64-akpm/drivers/char/mem.c 2004-07-31 20:57:35.141917576 -0700
@@ -380,7 +380,7 @@ static inline size_t read_zero_pagealign
if (vma->vm_start > addr || (vma->vm_flags & VM_WRITE) == 0)
goto out_up;
- if (vma->vm_flags & VM_SHARED)
+ if (vma->vm_flags & (VM_SHARED | VM_HUGETLB))
break;
count = vma->vm_end - addr;
if (count > size)
_