Re: init_on_free breaks hibernate

[Alexander Potapenko <glider@google.com>]

> > Strange about the resume=/dev/vda, it worked for me the way I described it.
> > Maybe device numbers are dynamic, 254:0 is what I got from ls -l /dev/vda.
> Indeed, for me it's 253:0, and resuming from console works with that number.
>
> > > The memory corruption is also reproducible for me, taking a look.
> >

I think I know what is causing the problem.
Upon resume the free pages may contain stale information from the
kernel that initiated the resume.
There's clear_free_pages()
(https://elixir.bootlin.com/linux/latest/source/kernel/power/snapshot.c#L1148)
that clears the pages in the case CONFIG_PAGE_POISONING_ZERO is
enabled, we just need to reuse it for init_on_free.
See the potential fix below.

Rafael, Pavel, I've noticed that in the setup suggested by Johannes
even the defconfig kernel with heap initialization cannot hibernate
more than twice, the third hibernate hangs.
Is that a known problem?

diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index 26b9168321e7..d65f2d5ab694 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -1147,24 +1147,24 @@ void free_basic_memory_bitmaps(void)

 void clear_free_pages(void)
 {
-#ifdef CONFIG_PAGE_POISONING_ZERO
        struct memory_bitmap *bm = free_pages_map;
        unsigned long pfn;

        if (WARN_ON(!(free_pages_map)))
                return;

-       memory_bm_position_reset(bm);
-       pfn = memory_bm_next_pfn(bm);
-       while (pfn != BM_END_OF_MAP) {
-               if (pfn_valid(pfn))
-                       clear_highpage(pfn_to_page(pfn));
-
+       if (IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) || want_init_on_free()) {
+               memory_bm_position_reset(bm);
                pfn = memory_bm_next_pfn(bm);
+               while (pfn != BM_END_OF_MAP) {
+                       if (pfn_valid(pfn))
+                               clear_highpage(pfn_to_page(pfn));
+
+                       pfn = memory_bm_next_pfn(bm);
+               }
+               memory_bm_position_reset(bm);
+               pr_info("free pages cleared after restore\n");
        }
-       memory_bm_position_reset(bm);
-       pr_info("free pages cleared after restore\n");
-#endif /* PAGE_POISONING_ZERO */
 }