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mm: vm_page_prot: update with WRITE_ONCE/READ_ONCE

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vma->vm_page_prot is read lockless from the rmap_walk, it may be updated
concurrently and this prevents the risk of reading intermediate values.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Andrea Arcangeli <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Jan Vorlicek <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Andrea Arcangeli 2016-10-07 17:01:22 -07:00 • committed by Linus Torvalds
commit 6d2329f887
5 changed files with 13 additions and 11 deletions
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16
mm/mmap.c
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@ -116,13 +116,15 @@ static pgprot_t vm_pgprot_modify(pgprot_t oldprot, unsigned long vm_flags)
void vma_set_page_prot(struct vm_area_struct *vma)
{
unsigned long vm_flags = vma->vm_flags;
pgprot_t vm_page_prot;
vma->vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, vm_flags);
if (vma_wants_writenotify(vma)) {
vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, vm_flags);
if (vma_wants_writenotify(vma, vm_page_prot)) {
vm_flags &= ~VM_SHARED;
vma->vm_page_prot = vm_pgprot_modify(vma->vm_page_prot,
vm_flags);
vm_page_prot = vm_pgprot_modify(vm_page_prot, vm_flags);
}
/* remove_protection_ptes reads vma->vm_page_prot without mmap_sem */
WRITE_ONCE(vma->vm_page_prot, vm_page_prot);
}
/*
@ -1386,7 +1388,7 @@ SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg)
* to the private version (using protection_map[] without the
* VM_SHARED bit).
*/
int vma_wants_writenotify(struct vm_area_struct *vma)
int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot)
{
vm_flags_t vm_flags = vma->vm_flags;
const struct vm_operations_struct *vm_ops = vma->vm_ops;
@ -1401,8 +1403,8 @@ int vma_wants_writenotify(struct vm_area_struct *vma)
/* The open routine did something to the protections that pgprot_modify
* won't preserve? */
if (pgprot_val(vma->vm_page_prot) !=
pgprot_val(vm_pgprot_modify(vma->vm_page_prot, vm_flags)))
if (pgprot_val(vm_page_prot) !=
pgprot_val(vm_pgprot_modify(vm_page_prot, vm_flags)))
return 0;
/* Do we need to track softdirty? */