From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S944818AbdEZT7p (ORCPT ); Fri, 26 May 2017 15:59:45 -0400 Received: from mga06.intel.com ([134.134.136.31]:53447 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934332AbdEZT7k (ORCPT ); Fri, 26 May 2017 15:59:40 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.38,399,1491289200"; d="scan'208";a="266874511" From: Ross Zwisler To: Andrew Morton , linux-kernel@vger.kernel.org Cc: Ross Zwisler , "Darrick J. Wong" , Alexander Viro , Christoph Hellwig , Dan Williams , Dave Hansen , Jan Kara , Matthew Wilcox , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-nvdimm@ml01.01.org, "Kirill A . Shutemov" , Pawel Lebioda , Dave Jiang , Xiong Zhou , Eryu Guan , stable@vger.kernel.org Subject: [PATCH] dax: improve fix for colliding PMD & PTE entries Date: Fri, 26 May 2017 13:59:32 -0600 Message-Id: <20170526195932.32178-1-ross.zwisler@linux.intel.com> X-Mailer: git-send-email 2.9.4 In-Reply-To: <20170522215749.23516-2-ross.zwisler@linux.intel.com> References: <20170522215749.23516-2-ross.zwisler@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This commit, which has not yet made it upstream but is in the -mm tree: dax: Fix race between colliding PMD & PTE entries fixed a pair of race conditions where racing DAX PTE and PMD faults could corrupt page tables. This fix had two shortcomings which are addressed by this patch: 1) In the PTE fault handler we only checked for a collision using pmd_devmap(). The pmd_devmap() check will trigger when we have raced with a PMD that has real DAX storage, but to account for the case where we collide with a huge zero page entry we also need to check for pmd_trans_huge(). 2) In the PMD fault handler we only continued with the fault if no PMD at all was present (pmd_none()). This is the case when we are faulting in a PMD for the first time, but there are two other cases to consider. The first is that we are servicing a write fault over a PMD huge zero page, which we detect with pmd_trans_huge(). The second is that we are servicing a write fault over a DAX PMD with real storage, which we address with pmd_devmap(). Fix both of these, and instead of manually triggering a fallback in the PMD collision case instead be consistent with the other collision detection code in the fault handlers and just retry. Signed-off-by: Ross Zwisler Cc: stable@vger.kernel.org --- For both the -mm tree and for stable, feel free to squash this with the original commit if you think that is appropriate. This has passed targeted testing and an xfstests run. --- fs/dax.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index fc62f36..2a6889b 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -1160,7 +1160,7 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, * the PTE we need to set up. If so just return and the fault will be * retried. */ - if (pmd_devmap(*vmf->pmd)) { + if (pmd_trans_huge(*vmf->pmd) || pmd_devmap(*vmf->pmd)) { vmf_ret = VM_FAULT_NOPAGE; goto unlock_entry; } @@ -1411,11 +1411,14 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf, /* * It is possible, particularly with mixed reads & writes to private * mappings, that we have raced with a PTE fault that overlaps with - * the PMD we need to set up. If so we just fall back to a PTE fault - * ourselves. + * the PMD we need to set up. If so just return and the fault will be + * retried. */ - if (!pmd_none(*vmf->pmd)) + if (!pmd_none(*vmf->pmd) && !pmd_trans_huge(*vmf->pmd) && + !pmd_devmap(*vmf->pmd)) { + result = 0; goto unlock_entry; + } /* * Note that we don't use iomap_apply here. We aren't doing I/O, only -- 2.9.4