4.19-stable review patch. If anyone has any objections, please let me know.
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commit 59e4293149106fb92530f8e56fa3992d8548c5e6 upstream.
Page writeback indirectly handles shared extents via the existence of overlapping COW fork blocks. If COW fork blocks exist, writeback always performs the associated copy-on-write regardless if the underlying blocks are actually shared. If the blocks are shared, then overlapping COW fork blocks must always exist.
fstests shared/010 reproduces a case where a buffered write occurs over a shared block without performing the requisite COW fork reservation. This ultimately causes writeback to the shared extent and data corruption that is detected across md5 checks of the filesystem across a mount cycle.
The problem occurs when a buffered write lands over a shared extent that crosses an extent size hint boundary and that also happens to have a partial COW reservation that doesn't cover the start and end blocks of the data fork extent.
For example, a buffered write occurs across the file offset (in FSB units) range of [29, 57]. A shared extent exists at blocks [29, 35] and COW reservation already exists at blocks [32, 34]. After accommodating a COW extent size hint of 32 blocks and the existing reservation at offset 32, xfs_reflink_reserve_cow() allocates 32 blocks of reservation at offset 0 and returns with COW reservation across the range of [0, 34]. The associated data fork extent is still [29, 35], however, which isn't fully covered by the COW reservation.
This leads to a buffered write at file offset 35 over a shared extent without associated COW reservation. Writeback eventually kicks in, performs an overwrite of the underlying shared block and causes the associated data corruption.
Update xfs_reflink_reserve_cow() to accommodate the fact that a delalloc allocation request may not fully cover the extent in the data fork. Trim the data fork extent appropriately, just as is done for shared extent boundaries and/or existing COW reservations that happen to overlap the start of the data fork extent. This prevents shared/010 failures due to data corruption on reflink enabled filesystems.
Signed-off-by: Brian Foster bfoster@redhat.com Reviewed-by: Christoph Hellwig hch@lst.de Reviewed-by: Darrick J. Wong darrick.wong@oracle.com Signed-off-by: Darrick J. Wong darrick.wong@oracle.com Signed-off-by: Luis Chamberlain mcgrof@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/xfs/xfs_reflink.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c index 42ea7bab9144..7088f44c0c59 100644 --- a/fs/xfs/xfs_reflink.c +++ b/fs/xfs/xfs_reflink.c @@ -302,6 +302,7 @@ xfs_reflink_reserve_cow( if (error) return error;
+ xfs_trim_extent(imap, got.br_startoff, got.br_blockcount); trace_xfs_reflink_cow_alloc(ip, &got); return 0; }