On Mon 02-07-18 11:27:45, Pavel Tatashin wrote:
> If struct page is poisoned, and uninitialized access is detected via
> PF_POISONED_CHECK(page) dump_page() is called to output the page. But,
> the dump_page() itself accesses struct page to determine how to print
> it, and therefore gets into a recursive loop.
>
> For example:
> dump_page()
> __dump_page()
> PageSlab(page)
> PF_POISONED_CHECK(page)
> VM_BUG_ON_PGFLAGS(PagePoisoned(page), page)
> dump_page() recursion loop.
This deserves a big fat comment in __dump_page. Basically no Page$FOO
can be used on an HWPoison page.
> Fixes: f165b378bbdf ("mm: uninitialized struct page poisoning sanity
> checking")
> Signed-off-by: Pavel Tatashin <[email protected]>
Acked-by: Michal Hocko <[email protected]>
> ---
> mm/debug.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/mm/debug.c b/mm/debug.c
> index 56e2d9125ea5..469b526e6abc 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -43,12 +43,20 @@ const struct trace_print_flags vmaflag_names[] = {
>
> void __dump_page(struct page *page, const char *reason)
> {
> + bool page_poisoned = PagePoisoned(page);
> + int mapcount;
> +
> + if (page_poisoned) {
> + pr_emerg("page:%px is uninitialized and poisoned", page);
> + goto hex_only;
> + }
> +
> /*
> * Avoid VM_BUG_ON() in page_mapcount().
> * page->_mapcount space in struct page is used by sl[aou]b pages to
> * encode own info.
> */
> - int mapcount = PageSlab(page) ? 0 : page_mapcount(page);
> + mapcount = PageSlab(page) ? 0 : page_mapcount(page);
>
> pr_emerg("page:%px count:%d mapcount:%d mapping:%px index:%#lx",
> page, page_ref_count(page), mapcount,
> @@ -60,6 +68,7 @@ void __dump_page(struct page *page, const char *reason)
>
> pr_emerg("flags: %#lx(%pGp)\n", page->flags, &page->flags);
>
> +hex_only:
> print_hex_dump(KERN_ALERT, "raw: ", DUMP_PREFIX_NONE, 32,
> sizeof(unsigned long), page,
> sizeof(struct page), false);
> @@ -68,7 +77,7 @@ void __dump_page(struct page *page, const char *reason)
> pr_alert("page dumped because: %s\n", reason);
>
> #ifdef CONFIG_MEMCG
> - if (page->mem_cgroup)
> + if (!page_poisoned && page->mem_cgroup)
> pr_alert("page->mem_cgroup:%px\n", page->mem_cgroup);
> #endif
> }
> --
> 2.18.0
>
--
Michal Hocko
SUSE Labs
