A compound page collects the refcount in the head page, while leaving the refcount of each tail page at zero. Therefore, when debugging a problem that involves compound pages, it's best to have diagnostics that reflect that situation. However, dump_page() is oblivious to these points.
Change dump_page() as follows:
1) For tail pages, print relevant head page information: refcount, in particular. But only do this if the page is not corrupted so badly that the pointer to the head page is all wrong.
2) Do a separate check to catch any (rare) cases of the tail page's refcount being non-zero, and issue a separate, clear pr_warn() if that ever happens.
Suggested-by: Matthew Wilcox willy@infradead.org Suggested-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Signed-off-by: John Hubbard jhubbard@nvidia.com --- mm/debug.c | 34 ++++++++++++++++++++++++++++------ 1 file changed, 28 insertions(+), 6 deletions(-)
diff --git a/mm/debug.c b/mm/debug.c index ecccd9f17801..beb1c59d784b 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -42,6 +42,32 @@ const struct trace_print_flags vmaflag_names[] = { {0, NULL} };
+static void __dump_tail_page(struct page *page, int mapcount) +{ + 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)); +} + void __dump_page(struct page *page, const char *reason) { struct address_space *mapping; @@ -75,12 +101,8 @@ 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)) + __dump_tail_page(page, mapcount); else pr_warn("page:%px refcount:%d mapcount:%d mapping:%px index:%#lx\n", page, page_ref_count(page), mapcount,