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From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: darrick.wong@oracle.com
Cc: Christoph Hellwig <hch@lst.de>, Brian Foster <bfoster@redhat.com>,
	linux-xfs@vger.kernel.org, hch@infradead.org, bfoster@redhat.com
Subject: [PATCH 4/4] xfs: force writes to delalloc regions to unwritten
Date: Sat, 23 May 2020 09:49:58 -0700
Message-ID: <159025259804.493629.14105390886258058200.stgit@magnolia> (raw)
In-Reply-To: <159025257178.493629.12621189512718182426.stgit@magnolia>

From: Darrick J. Wong <darrick.wong@oracle.com>

When writing to a delalloc region in the data fork, commit the new
allocations (of the da reservation) as unwritten so that the mappings
are only marked written once writeback completes successfully.  This
fixes the problem of stale data exposure if the system goes down during
targeted writeback of a specific region of a file, as tested by
generic/042.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
---
 fs/xfs/libxfs/xfs_bmap.c |   29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)


diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index fda13cd7add0..f8fe83c9348d 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -4193,17 +4193,7 @@ xfs_bmapi_allocate(
 	bma->got.br_blockcount = bma->length;
 	bma->got.br_state = XFS_EXT_NORM;
 
-	/*
-	 * In the data fork, a wasdelay extent has been initialized, so
-	 * shouldn't be flagged as unwritten.
-	 *
-	 * For the cow fork, however, we convert delalloc reservations
-	 * (extents allocated for speculative preallocation) to
-	 * allocated unwritten extents, and only convert the unwritten
-	 * extents to real extents when we're about to write the data.
-	 */
-	if ((!bma->wasdel || (bma->flags & XFS_BMAPI_COWFORK)) &&
-	    (bma->flags & XFS_BMAPI_PREALLOC))
+	if (bma->flags & XFS_BMAPI_PREALLOC)
 		bma->got.br_state = XFS_EXT_UNWRITTEN;
 
 	if (bma->wasdel)
@@ -4611,8 +4601,23 @@ xfs_bmapi_convert_delalloc(
 	bma.offset = bma.got.br_startoff;
 	bma.length = max_t(xfs_filblks_t, bma.got.br_blockcount, MAXEXTLEN);
 	bma.minleft = xfs_bmapi_minleft(tp, ip, whichfork);
+
+	/*
+	 * When we're converting the delalloc reservations backing dirty pages
+	 * in the page cache, we must be careful about how we create the new
+	 * extents:
+	 *
+	 * New CoW fork extents are created unwritten, turned into real extents
+	 * when we're about to write the data to disk, and mapped into the data
+	 * fork after the write finishes.  End of story.
+	 *
+	 * New data fork extents must be mapped in as unwritten and converted
+	 * to real extents after the write succeeds to avoid exposing stale
+	 * disk contents if we crash.
+	 */
+	bma.flags = XFS_BMAPI_PREALLOC;
 	if (whichfork == XFS_COW_FORK)
-		bma.flags = XFS_BMAPI_COWFORK | XFS_BMAPI_PREALLOC;
+		bma.flags |= XFS_BMAPI_COWFORK;
 
 	if (!xfs_iext_peek_prev_extent(ifp, &bma.icur, &bma.prev))
 		bma.prev.br_startoff = NULLFILEOFF;


  parent reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-23 16:49 [PATCH v4 0/4] xfs: fix stale disk exposure after crash Darrick J. Wong
2020-05-23 16:49 ` [PATCH 1/4] xfs: don't fail unwritten extent conversion on writeback due to edquot Darrick J. Wong
2020-05-23 16:49 ` [PATCH 2/4] xfs: measure all contiguous previous extents for prealloc size Darrick J. Wong
2020-05-24  9:14   ` Christoph Hellwig
2020-05-24 17:16     ` Darrick J. Wong
2020-05-24 17:16   ` [PATCH v2 " Darrick J. Wong
2020-05-25 13:28     ` Christoph Hellwig
2020-05-26 13:46     ` Brian Foster
2020-05-23 16:49 ` [PATCH 3/4] xfs: refactor xfs_iomap_prealloc_size Darrick J. Wong
2020-05-24 17:17   ` [PATCH v2 " Darrick J. Wong
2020-05-26 13:46     ` Brian Foster
2020-05-23 16:49 ` Darrick J. Wong [this message]
  -- strict thread matches above, loose matches on Subject: below --
2020-05-22  2:52 [PATCH v3 0/4] xfs: fix stale disk exposure after crash Darrick J. Wong
2020-05-22  2:53 ` [PATCH 4/4] xfs: force writes to delalloc regions to unwritten Darrick J. Wong
2020-05-22  3:31   ` Dave Chinner
2020-05-22  3:56     ` Darrick J. Wong

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