| Message ID | 20180702180536.2552-1-pasha.tatashin@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon 02-07-18 14:05:36, Pavel Tatashin wrote: [...] > 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; > + } Thanks for the updated comment. Exactly what I was looking for!
On Mon, 2 Jul 2018 14:05:36 -0400 Pavel Tatashin <pasha.tatashin@oracle.com> 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. > > 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> Thanks. I added a cc:stable to make sure this gets into 4.17.x.
diff --git a/mm/debug.c b/mm/debug.c index 56e2d9125ea5..38c926520c97 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -43,12 +43,25 @@ const struct trace_print_flags vmaflag_names[] = { 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, 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 +82,7 @@ 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 }
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. 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> --- mm/debug.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-)