On 1/29/20 2:59 PM, Matthew Wilcox wrote: ...
I have a hunk in my current tree which looks like this:
@@ -77,6 +77,11 @@ void __dump_page(struct page *page, const char *reason) pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx \n", page, page_ref_count(page), mapcount, page->mapping, page_to_pgoff(page));
if (PageTail(page)) {struct page *head = compound_head(page);pr_warn("head:%px mapping:%px index:%#lx\n",head, head->mapping, page_to_pgoff(head));} if (PageKsm(page)) pr_warn("ksm flags: %#lx(%pGp)\n", page->flags, &page->flags); else if (PageAnon(page))I wonder if we can combine these two patches in some more useful way?
I also think we probably want a sanity check that 'head' and 'page' are within a sane range of each other (ie head < page and head + MAX_ORDER_NR_PAGES > page) to protect against a struct page that contains complete garbage.
OK, here's a go at combining those. I like the observation, implicit in your diffs, that PageTail rather than PageCompound is the key differentiator in deciding what to print. How's this look:
diff --git a/mm/debug.c b/mm/debug.c index a90da5337c14..944652843e7b 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -75,12 +75,31 @@ void __dump_page(struct page *page, const char *reason) */ mapcount = PageSlab(page) ? 0 : page_mapcount(page);
- if (PageCompound(page)) - pr_warn("page:%px refcount:%d mapcount:%d mapping:%px " - "index:%#lx compound_mapcount: %d\n", - page, page_ref_count(page), mapcount, - page->mapping, page_to_pgoff(page), - compound_mapcount(page)); + if (PageTail(page)) { + struct page *head = compound_head(page); + + if ((page < head) || (page >= head + MAX_ORDER_NR_PAGES)) { + /* + * Page is hopelessly corrupted, so limit any reporting + * to information about the page itself. Do not attempt + * to look at the head page. + */ + pr_warn("page:%px refcount:%d mapcount:%d mapping:%px " + "index:%#lx (corrupted tail page case)\n", + page, page_ref_count(page), mapcount, + page->mapping, page_to_pgoff(page)); + } else { + pr_warn("page:%px compound refcount:%d mapcount:%d " + "mapping:%px index:%#lx compound_mapcount:%d\n", + page, page_ref_count(head), + mapcount, head->mapping, page_to_pgoff(head), + compound_mapcount(page)); + + if (page_ref_count(page) != 0) + pr_warn("page:%px PROBLEM: non-zero refcount (==%d) on " + "this tail page\n", page, page_ref_count(page)); + } + } else pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx\n", page, page_ref_count(page), mapcount,
?
Here's sample output for a normal page, a tail page, and a tail page with a bad (non-zero) refcount:
============ Normal page: ============ [ 38.572084] page:ffffea0011465880 refcount:2 mapcount:1 mapping:ffff888454d99001 index:0xb2 [ 38.579256] anon flags: 0x17ffe0000080036(referenced|uptodate|lru|active|swapbacked) [ 38.585799] raw: 017ffe0000080036 ffffea0011460fc8 ffffea0011466d08 ffff888454d99001 [ 38.592350] raw: 00000000000000b2 0000000000000000 0000000200000000 0000000000000000 [ 38.598885] page dumped because: test dump page
========== Tail page: ========== [ 38.436384] page:ffffea0010aa0280 compound refcount:503 mapcount:1 mapping:ffff888455fb3399 index:0xa8 compound_mapcount:1 [ 38.446350] anon flags: 0x17ffe0000000000() [ 38.449661] raw: 017ffe0000000000 ffffea0010aa0001 ffffea0010aa0288 dead000000000400 [ 38.456228] raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000 [ 38.462794] page dumped because: test dump page
============================ Tail page with bad refcount: ============================ [ 38.466088] page:ffffea0010aa0b40 compound refcount:468 mapcount:1 mapping:ffff888455fb3399 index:0xa8 compound_mapcount:1 [ 38.475967] page:ffffea0010aa0b40 PROBLEM: non-zero refcount (==2) on this tail page [ 38.482490] anon flags: 0x17ffe0000000000() [ 38.485432] raw: 017ffe0000000000 ffffea0010aa0001 ffffea0010aa0b48 dead000000000400 [ 38.491996] raw: 0000000000000000 0000000000000000 00000002ffffffff 0000000000000000 [ 38.498532] page dumped because: test bad tail page refcount
thanks,