From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752000AbbJEUdH (ORCPT ); Mon, 5 Oct 2015 16:33:07 -0400 Received: from mga09.intel.com ([134.134.136.24]:5306 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750892AbbJEUdF (ORCPT ); Mon, 5 Oct 2015 16:33:05 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.17,640,1437462000"; d="scan'208";a="819995350" From: Ross Zwisler To: linux-kernel@vger.kernel.org Cc: Ross Zwisler , Alexander Viro , Matthew Wilcox , linux-fsdevel@vger.kernel.org, Andrew Morton , Dan Williams , Dave Chinner , Jan Kara , "Kirill A. Shutemov" , linux-nvdimm@ml01.01.org Subject: [PATCH v3 3/3] dax: temporarily disable DAX PMD fault path Date: Mon, 5 Oct 2015 14:32:54 -0600 Message-Id: <1444077174-22016-4-git-send-email-ross.zwisler@linux.intel.com> X-Mailer: git-send-email 2.1.0 In-Reply-To: <1444077174-22016-1-git-send-email-ross.zwisler@linux.intel.com> References: <1444077174-22016-1-git-send-email-ross.zwisler@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org There is currently a deadlock in the DAX PMD fault path because it ends up taking the same mapping->i_mmap_rwsem twice. The first take is a i_mmap_lock_read() near the beginning of __dax_pmd_fault(), and the second is __dax_pmd_fault() -> unmap_mapping_range() -> i_mmap_lock_write(). We are re-working the way that DAX does its locking for v4.4, so for now just disable DAX PMD faults and fall back to PAGE_SIZE faults to make sure we don't hit this deadlock. Signed-off-by: Ross Zwisler --- fs/dax.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/dax.c b/fs/dax.c index f364c90..d42217d 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -534,6 +534,13 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, unsigned long pfn; int result = 0; + /* + * There is currently a deadlock in the DAX PMD fault path. Disable + * this path and fall back to the normal dax_fault() path for now + * while we rework locking. + */ + return VM_FAULT_FALLBACK; + /* Fall back to PTEs if we're going to COW */ if (write && !(vma->vm_flags & VM_SHARED)) return VM_FAULT_FALLBACK; -- 2.1.0