On 1/29/20 10:23 PM, John Hubbard wrote:
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));
...ahem, I sorta botched the above statement, because that should be outside (just below) the "else" statement--it can be done whether or not the page fails the safety/bounds check. :) thanks, -- John Hubbard NVIDIA
