Make it clear what we're blocking in MADV_DOFORK. Previously we simply
disallowed VM_SPECIAL i.e. kernel-owned mappings, fixed mappings and
VMA_IO_BIT.
Now the invariant is established that only kernel-owned mappings can set
VMA_IO_BIT, the VMA_IO_BIT check is redundant.
The rest is equivalent to testing for a kernel-owned or fixed mapping,
i.e. exactly the same check as whether the VMA is permitted to be merged.
This was established by commit 0b2758f48f22 ("Require (reasonably) normal
mappings for MADV_DOFORK") containing my hands-down favourite call out of
all time.
Express the same thing differently - if we wouldn't be allowed to merge it,
then we aren't allowed to manipulate CoW behaviour on fork.
No functional change intended.
Signed-off-by: Lorenzo Stoakes (ARM) <[email protected]>
---
mm/madvise.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/madvise.c b/mm/madvise.c
index e15973292f94..1af82b044d23 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1565,7 +1565,7 @@ static int madvise_vma_behavior(struct madvise_behavior
*madv_behavior)
new_flags |= VM_DONTCOPY;
break;
case MADV_DOFORK:
- if (new_flags & VM_SPECIAL)
+ if (!vma_can_merge(vma))
return -EINVAL;
new_flags &= ~VM_DONTCOPY;
break;
--
2.55.0
