Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752018AbbKQKkX (ORCPT ); Tue, 17 Nov 2015 05:40:23 -0500 Received: from mail-wm0-f46.google.com ([74.125.82.46]:34454 "EHLO mail-wm0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751144AbbKQKkU (ORCPT ); Tue, 17 Nov 2015 05:40:20 -0500 Message-ID: <564B0410.9040502@plexistor.com> Date: Tue, 17 Nov 2015 12:40:16 +0200 From: Boaz Harrosh User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Ross Zwisler , Dan Williams , Yigal Korman , "linux-kernel@vger.kernel.org" , "linux-nvdimm@lists.01.org" , Linux MM , linux-fsdevel , david , Andrew Morton , Stable Tree , Alexander Viro , Dave Chinner , Jan Kara , "Kirill A. Shutemov" , Matthew Wilcox Subject: Re: [PATCH] mm, dax: fix DAX deadlocks (COW fault) References: <1447675755-5692-1-git-send-email-yigal@plexistor.com> <20151116183404.GA22996@linux.intel.com> In-Reply-To: <20151116183404.GA22996@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3527 Lines: 83 On 11/16/2015 08:34 PM, Ross Zwisler wrote: > On Mon, Nov 16, 2015 at 10:15:56AM -0800, Dan Williams wrote: >> On Mon, Nov 16, 2015 at 4:09 AM, Yigal Korman wrote: >>> DAX handling of COW faults has wrong locking sequence: >>> dax_fault does i_mmap_lock_read >>> do_cow_fault does i_mmap_unlock_write >>> >>> Ross's commit[1] missed a fix[2] that Kirill added to Matthew's >>> commit[3]. >>> >>> Original COW locking logic was introduced by Matthew here[4]. >>> >>> This should be applied to v4.3 as well. >>> >>> [1] 0f90cc6609c7 mm, dax: fix DAX deadlocks >>> [2] 52a2b53ffde6 mm, dax: use i_mmap_unlock_write() in do_cow_fault() >>> [3] 843172978bb9 dax: fix race between simultaneous faults >>> [4] 2e4cdab0584f mm: allow page fault handlers to perform the COW >>> >>> Signed-off-by: Yigal Korman >>> >>> Cc: Stable Tree >>> Cc: Boaz Harrosh >>> Cc: Ross Zwisler >>> Cc: Alexander Viro >>> Cc: Dan Williams >>> Cc: Dave Chinner >>> Cc: Jan Kara >>> Cc: "Kirill A. Shutemov" >>> Cc: Matthew Wilcox >>> --- >>> mm/memory.c | 8 ++++---- >>> 1 file changed, 4 insertions(+), 4 deletions(-) >>> >>> diff --git a/mm/memory.c b/mm/memory.c >>> index c716913..e5071af 100644 >>> --- a/mm/memory.c >>> +++ b/mm/memory.c >>> @@ -3015,9 +3015,9 @@ static int do_cow_fault(struct mm_struct *mm, struct vm_area_struct *vma, >>> } else { >>> /* >>> * The fault handler has no page to lock, so it holds >>> - * i_mmap_lock for write to protect against truncate. >>> + * i_mmap_lock for read to protect against truncate. >>> */ >>> - i_mmap_unlock_write(vma->vm_file->f_mapping); >>> + i_mmap_unlock_read(vma->vm_file->f_mapping); >>> } >>> goto uncharge_out; >>> } >>> @@ -3031,9 +3031,9 @@ static int do_cow_fault(struct mm_struct *mm, struct vm_area_struct *vma, >>> } else { >>> /* >>> * The fault handler has no page to lock, so it holds >>> - * i_mmap_lock for write to protect against truncate. >>> + * i_mmap_lock for read to protect against truncate. >>> */ >>> - i_mmap_unlock_write(vma->vm_file->f_mapping); >>> + i_mmap_unlock_read(vma->vm_file->f_mapping); >>> } >>> return ret; >>> uncharge_out: >> >> Looks good to me. I'll include this with some other DAX fixes I have pending. > > Looks good to me as well. Thanks for catching this. > Yes. None of the xfstests catch this. It needs a private-mapping mmap in some combination of other activity on the file at the same time. Which the linker of gcc does. We have a test of a git clone Kernel-tree and make. which catches this in the make phase. For some reason on ext4 it is reliable to crash but on xfs 1/2 the runs go through, go figure. Thanks Yigal for the fast fix Boaz -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/