From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f199.google.com (mail-pg1-f199.google.com [209.85.215.199]) by kanga.kvack.org (Postfix) with ESMTP id ADD006B0007 for ; Tue, 13 Nov 2018 00:50:12 -0500 (EST) Received: by mail-pg1-f199.google.com with SMTP id s22so7359668pgv.8 for ; Mon, 12 Nov 2018 21:50:12 -0800 (PST) Received: from mail.kernel.org (mail.kernel.org. [198.145.29.99]) by mx.google.com with ESMTPS id k11si19315938pgf.213.2018.11.12.21.50.11 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 12 Nov 2018 21:50:11 -0800 (PST) From: Sasha Levin Subject: [PATCH AUTOSEL 4.19 13/44] mm: Fix warning in insert_pfn() Date: Tue, 13 Nov 2018 00:49:19 -0500 Message-Id: <20181113054950.77898-13-sashal@kernel.org> In-Reply-To: <20181113054950.77898-1-sashal@kernel.org> References: <20181113054950.77898-1-sashal@kernel.org> Sender: owner-linux-mm@kvack.org List-ID: To: stable@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Jan Kara , Ross Zwisler , Dan Williams , Dave Jiang , Andrew Morton , Linus Torvalds , Sasha Levin , linux-mm@kvack.org From: Jan Kara [ Upstream commit f2c57d91b0d96aa13ccff4e3b178038f17b00658 ] In DAX mode a write pagefault can race with write(2) in the following way: CPU0 CPU1 write fault for mapped zero page (hole) dax_iomap_rw() iomap_apply() xfs_file_iomap_begin() - allocates blocks dax_iomap_actor() invalidate_inode_pages2_range() - invalidates radix tree entries in given range dax_iomap_pte_fault() grab_mapping_entry() - no entry found, creates empty ... xfs_file_iomap_begin() - finds already allocated block ... vmf_insert_mixed_mkwrite() - WARNs and does nothing because there is still zero page mapped in PTE unmap_mapping_pages() This race results in WARN_ON from insert_pfn() and is occasionally triggered by fstest generic/344. Note that the race is otherwise harmless as before write(2) on CPU0 is finished, we will invalidate page tables properly and thus user of mmap will see modified data from write(2) from that point on. So just restrict the warning only to the case when the PFN in PTE is not zero page. Link: http://lkml.kernel.org/r/20180824154542.26872-1-jack@suse.cz Signed-off-by: Jan Kara Reviewed-by: Andrew Morton Cc: Ross Zwisler Cc: Dan Williams Cc: Dave Jiang Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- mm/memory.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index c467102a5cbc..d988bae46479 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1787,10 +1787,15 @@ static int insert_pfn(struct vm_area_struct *vma, unsigned long addr, * in may not match the PFN we have mapped if the * mapped PFN is a writeable COW page. In the mkwrite * case we are creating a writable PTE for a shared - * mapping and we expect the PFNs to match. + * mapping and we expect the PFNs to match. If they + * don't match, we are likely racing with block + * allocation and mapping invalidation so just skip the + * update. */ - if (WARN_ON_ONCE(pte_pfn(*pte) != pfn_t_to_pfn(pfn))) + if (pte_pfn(*pte) != pfn_t_to_pfn(pfn)) { + WARN_ON_ONCE(!is_zero_pfn(pte_pfn(*pte))); goto out_unlock; + } entry = *pte; goto out_mkwrite; } else -- 2.17.1