From: Darrick J. Wong <darrick.wong@xxxxxxxxxx> 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@xxxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> --- fs/xfs/libxfs/xfs_bmap.c | 28 +++++++++++++++++----------- 1 file changed, 17 insertions(+), 11 deletions(-) diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c index fda13cd7add0..825d170e1503 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 +4601,24 @@ 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. + */ if (whichfork == XFS_COW_FORK) bma.flags = XFS_BMAPI_COWFORK | XFS_BMAPI_PREALLOC; + else + bma.flags = XFS_BMAPI_PREALLOC; if (!xfs_iext_peek_prev_extent(ifp, &bma.icur, &bma.prev)) bma.prev.br_startoff = NULLFILEOFF;
