From: Pavel Tatashin pasha.tatashin@oracle.com Subject: mm: teach dump_page() to correctly output poisoned struct pages

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.

Link: http://lkml.kernel.org/r/20180702180536.2552-1-pasha.tatashin@oracle.com Fixes: f165b378bbdf ("mm: uninitialized struct page poisoning sanity checking") Signed-off-by: Pavel Tatashin pasha.tatashin@oracle.com Acked-by: Michal Hocko mhocko@suse.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/debug.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-)

diff -puN mm/debug.c~mm-teach-dump_page-to-correctly-output-poisoned-struct-pages mm/debug.c --- a/mm/debug.c~mm-teach-dump_page-to-correctly-output-poisoned-struct-pages +++ a/mm/debug.c @@ -43,12 +43,25 @@ const struct trace_print_flags vmaflag_n

void __dump_page(struct page *page, const char *reason) { + bool page_poisoned = PagePoisoned(page); + int mapcount; + + /* + * If struct page is poisoned don't access Page*() functions as that + * leads to recursive loop. Page*() check for poisoned pages, and calls + * dump_page() when detected. + */ + 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 +73,7 @@ void __dump_page(struct page *page, cons

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 +82,7 @@ void __dump_page(struct page *page, cons 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 } _