From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga05.intel.com ([192.55.52.43]:60844 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726666AbeHJVyR (ORCPT ); Fri, 10 Aug 2018 17:54:17 -0400 Subject: Re: [PATCH v2 2/2] [PATCH] xfs: Close race between direct IO and xfs_break_layouts() References: <153374942137.42241.10539674028265137668.stgit@djiang5-desk3.ch.intel.com> From: Dave Jiang Message-ID: Date: Fri, 10 Aug 2018 12:23:04 -0700 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: sandeen@redhat.com, tytso@mit.edu, darrick.wong@oracle.com, jack@suse.cz, zwisler@kernel.org Cc: linux-nvdimm@lists.01.org, david@fromorbit.com, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, lczerner@redhat.com, linux-ext4@vger.kernel.org, hch@lst.de On 08/10/2018 11:31 AM, Eric Sandeen wrote: > On 8/8/18 12:31 PM, Dave Jiang wrote: >> This patch is the duplicate of ross's fix for ext4 for xfs. >> >> If the refcount of a page is lowered between the time that it is returned >> by dax_busy_page() and when the refcount is again checked in >> xfs_break_layouts() => ___wait_var_event(), the waiting function >> xfs_wait_dax_page() will never be called. This means that >> xfs_break_layouts() will still have 'retry' set to false, so we'll stop >> looping and never check the refcount of other pages in this inode. >> >> Instead, always continue looping as long as dax_layout_busy_page() gives us >> a page which it found with an elevated refcount. > > Hi Dave, does this have a testcase? Have you seen the issue using Ross's > xfstest generic/503 or is there some other test? Apologies if I missed > prior discussion on a testcase or race frequency... I do not have a testcase. I know Ross replicated it on ext4. And Jan asked to create the same fix with XFS when he reviewed Ross's fix for ext4. > > Thanks, > -Eric > >> Signed-off-by: Dave Jiang >> Reviewed-by: Jan Kara >> --- >> >> Sorry resend, forgot to add Jan's reviewed-by. >> >> v2: >> - Rename parameter from did_unlock to retry (Jan) >> >> fs/xfs/xfs_file.c | 9 ++++----- >> 1 file changed, 4 insertions(+), 5 deletions(-) >> >> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c >> index a3e7767a5715..cd6f0d8c4922 100644 >> --- a/fs/xfs/xfs_file.c >> +++ b/fs/xfs/xfs_file.c >> @@ -721,12 +721,10 @@ xfs_file_write_iter( >> >> static void >> xfs_wait_dax_page( >> - struct inode *inode, >> - bool *did_unlock) >> + struct inode *inode) >> { >> struct xfs_inode *ip = XFS_I(inode); >> >> - *did_unlock = true; >> xfs_iunlock(ip, XFS_MMAPLOCK_EXCL); >> schedule(); >> xfs_ilock(ip, XFS_MMAPLOCK_EXCL); >> @@ -736,7 +734,7 @@ static int >> xfs_break_dax_layouts( >> struct inode *inode, >> uint iolock, >> - bool *did_unlock) >> + bool *retry) >> { >> struct page *page; >> >> @@ -746,9 +744,10 @@ xfs_break_dax_layouts( >> if (!page) >> return 0; >> >> + *retry = true; >> return ___wait_var_event(&page->_refcount, >> atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE, >> - 0, 0, xfs_wait_dax_page(inode, did_unlock)); >> + 0, 0, xfs_wait_dax_page(inode)); >> } >> >> int >>