From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp2120.oracle.com ([156.151.31.85]:60870 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726226AbfARF3d (ORCPT ); Fri, 18 Jan 2019 00:29:33 -0500 Subject: Re: [PATCH v2 1/5] xfs: eof trim writeback mapping as soon as it is cached References: <20190117192004.49346-1-bfoster@redhat.com> <20190117192004.49346-2-bfoster@redhat.com> From: Allison Henderson Message-ID: Date: Thu, 17 Jan 2019 22:29:22 -0700 MIME-Version: 1.0 In-Reply-To: <20190117192004.49346-2-bfoster@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Brian Foster , linux-xfs@vger.kernel.org On 1/17/19 12:20 PM, Brian Foster wrote: > The cached writeback mapping is EOF trimmed to try and avoid races > between post-eof block management and writeback that result in > sending cached data to a stale location. The cached mapping is > currently trimmed on the validation check, which leaves a race > window between the time the mapping is cached and when it is trimmed > against the current inode size. > > For example, if a new mapping is cached by delalloc conversion on a > blocksize == page size fs, we could cycle various locks, perform > memory allocations, etc. in the writeback codepath before the > associated mapping is eventually trimmed to i_size. This leaves > enough time for a post-eof truncate and file append before the > cached mapping is trimmed. The former event essentially invalidates > a range of the cached mapping and the latter bumps the inode size > such the trim on the next writepage event won't trim all of the > invalid blocks. fstest generic/464 reproduces this scenario > occasionally and causes a lost writeback and stale delalloc blocks > warning on inode inactivation. > > To work around this problem, trim the cached writeback mapping as > soon as it is cached in addition to on subsequent validation checks. > This is a minor tweak to tighten the race window as much as possible > until a proper invalidation mechanism is available. > > Fixes: 40214d128e07 ("xfs: trim writepage mapping to within eof") > Cc: # v4.14+ > Signed-off-by: Brian Foster > --- > fs/xfs/xfs_aops.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c > index 338b9d9984e0..d9048bcea49c 100644 > --- a/fs/xfs/xfs_aops.c > +++ b/fs/xfs/xfs_aops.c > @@ -449,6 +449,7 @@ xfs_map_blocks( > } > > wpc->imap = imap; > + xfs_trim_extent_eof(&wpc->imap, ip); > trace_xfs_map_blocks_found(ip, offset, count, wpc->io_type, &imap); > return 0; > allocate_blocks: > @@ -459,6 +460,7 @@ xfs_map_blocks( > ASSERT(whichfork == XFS_COW_FORK || cow_fsb == NULLFILEOFF || > imap.br_startoff + imap.br_blockcount <= cow_fsb); > wpc->imap = imap; > + xfs_trim_extent_eof(&wpc->imap, ip); > trace_xfs_map_blocks_alloc(ip, offset, count, wpc->io_type, &imap); > return 0; > } > Looks ok, you can add my review: Reviewed-by: Allison Henderson