Several times while testing swapless page migration, gcc has tried to
exec a pointer instead of a string: smells like COW mappings are not
being properly write-protected on fork.
The protection in copy_one_pte looks very convincing, until at last you
realize that the second arg to make_migration_entry is a boolean "write",
and SWP_MIGRATION_READ is 30.
Anyway, it's better done like in change_pte_range, using
is_write_migration_entry and make_migration_entry_read.
Signed-off-by: Hugh Dickins <[email protected]>
---
This is a fix to -mm's swapless-pm-add-r-w-migration-entries.patch
mm/memory.c | 9 +++------
1 file changed, 3 insertions(+), 6 deletions(-)
--- 2.6.17-rc4-mm3/mm/memory.c 2006-05-22 12:19:00.000000000 +0100
+++ linux/mm/memory.c 2006-05-26 16:31:59.000000000 +0100
@@ -448,16 +448,13 @@ copy_one_pte(struct mm_struct *dst_mm, s
&src_mm->mmlist);
spin_unlock(&mmlist_lock);
}
- if (is_migration_entry(entry) &&
+ if (is_write_migration_entry(entry) &&
is_cow_mapping(vm_flags)) {
- page = migration_entry_to_page(entry);
-
/*
* COW mappings require pages in both parent
- * and child to be set to read.
+ * and child to be set to read.
*/
- entry = make_migration_entry(page,
- SWP_MIGRATION_READ);
+ make_migration_entry_read(&entry);
pte = swp_entry_to_pte(entry);
set_pte_at(src_mm, addr, src_pte, pte);
}
-
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