From 27a83a609b3b39b0a4ec6c75050b1183d7c302db Mon Sep 17 00:00:00 2001 From: "Matthew Wilcox (Oracle)" Date: Tue, 13 Oct 2020 16:51:44 -0700 Subject: [PATCH] mm/filemap: fix filemap_map_pages for THP We dereference page->mapping and page->index directly after calling find_subpage() and these fields are not valid for tail pages. While commit 4101196b19d7 ("mm: page cache: store only head pages in i_pages") introduced the call to find_subpage(), the problem existed prior to this; I'm going to suggest all the way back to when THPs first existed. The user-visible effects of this are almost negligible. To hit it, you have to mmap a tmpfs file at an unaligned address and then it's only a disabled optimisation causing page faults to happen more frequently than they otherwise would. Fix this by keeping both head and page pointers and checking the appropriate one. We could use page_mapping() and page_to_index(), but that's higher overhead. Signed-off-by: Matthew Wilcox (Oracle) Signed-off-by: Andrew Morton Acked-by: Kirill A. Shutemov Cc: William Kucharski Link: https://lkml.kernel.org/r/20200911012532.24761-1-willy@infradead.org Signed-off-by: Linus Torvalds --- mm/filemap.c | 30 +++++++++++++++--------------- 1 file changed, 15 insertions(+), 15 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 63d2fed539d7..38546dca58fe 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2793,42 +2793,42 @@ void filemap_map_pages(struct vm_fault *vmf, pgoff_t last_pgoff = start_pgoff; unsigned long max_idx; XA_STATE(xas, &mapping->i_pages, start_pgoff); - struct page *page; + struct page *head, *page; unsigned int mmap_miss = READ_ONCE(file->f_ra.mmap_miss); rcu_read_lock(); - xas_for_each(&xas, page, end_pgoff) { - if (xas_retry(&xas, page)) + xas_for_each(&xas, head, end_pgoff) { + if (xas_retry(&xas, head)) continue; - if (xa_is_value(page)) + if (xa_is_value(head)) goto next; /* * Check for a locked page first, as a speculative * reference may adversely influence page migration. */ - if (PageLocked(page)) + if (PageLocked(head)) goto next; - if (!page_cache_get_speculative(page)) + if (!page_cache_get_speculative(head)) goto next; /* Has the page moved or been split? */ - if (unlikely(page != xas_reload(&xas))) + if (unlikely(head != xas_reload(&xas))) goto skip; - page = find_subpage(page, xas.xa_index); + page = find_subpage(head, xas.xa_index); - if (!PageUptodate(page) || + if (!PageUptodate(head) || PageReadahead(page) || PageHWPoison(page)) goto skip; - if (!trylock_page(page)) + if (!trylock_page(head)) goto skip; - if (page->mapping != mapping || !PageUptodate(page)) + if (head->mapping != mapping || !PageUptodate(head)) goto unlock; max_idx = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE); - if (page->index >= max_idx) + if (xas.xa_index >= max_idx) goto unlock; if (mmap_miss > 0) @@ -2840,12 +2840,12 @@ void filemap_map_pages(struct vm_fault *vmf, last_pgoff = xas.xa_index; if (alloc_set_pte(vmf, page)) goto unlock; - unlock_page(page); + unlock_page(head); goto next; unlock: - unlock_page(page); + unlock_page(head); skip: - put_page(page); + put_page(head); next: /* Huge page is mapped? No need to proceed. */ if (pmd_trans_huge(*vmf->pmd))