Hi Pavel,
This strikes me as wrong:
#define PF_HEAD(page, enforce) PF_POISONED_CHECK(compound_head(page))
If we hit a page which is poisoned, PAGE_POISON_PATTERN is ~0, so PageTail
is set, and compound_head will return() 0xfff..ffe. PagePoisoned()
will then try to derefence that pointer and we'll get an oops that isn't
obviously PagePoisoned.
I think this should have been:
#define PF_HEAD(page, enforce) compound_head(PF_POISONED_CHECK(page))
One could make the argument for double-checking:
#define PF_HEAD(page, enforce) PF_POISONED_CHECK(compound_head(PF_POISONED_CHECK(page)))
but I think this is overkill; if a tail page is initialised, then there's
no way that its head page should have been uninitialised.
Would a patch something along these lines make sense? Compile-tested only.
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 9f8712a4b1a5..1d25d0899854 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -227,16 +227,18 @@ static inline void page_init_poison(struct page *page, size_t size)
VM_BUG_ON_PGFLAGS(PagePoisoned(page), page); \
page; })
#define PF_ANY(page, enforce) PF_POISONED_CHECK(page)
-#define PF_HEAD(page, enforce) PF_POISONED_CHECK(compound_head(page))
+#define PF_HEAD(page, enforce) compound_head(PF_POISONED_CHECK(page))
#define PF_ONLY_HEAD(page, enforce) ({ \
+ PF_POISONED_CHECK(page); \
VM_BUG_ON_PGFLAGS(PageTail(page), page); \
- PF_POISONED_CHECK(page); })
+ page; })
#define PF_NO_TAIL(page, enforce) ({ \
VM_BUG_ON_PGFLAGS(enforce && PageTail(page), page); \
- PF_POISONED_CHECK(compound_head(page)); })
+ compound_head(PF_POISONED_CHECK(page)); })
#define PF_NO_COMPOUND(page, enforce) ({ \
+ PF_POISONED_CHECK(page); \
VM_BUG_ON_PGFLAGS(enforce && PageCompound(page), page); \
- PF_POISONED_CHECK(page); })
+ page; })
/*
* Macros to create function definitions for page flags
