[PATCH] xfs: restore shutdown check in mapped write fault path

[Brian Foster <bfoster@redhat.com>]

XFS triggers an iomap warning in the write fault path due to a
!PageUptodate() page if a write fault happens to occur on a page
that recently failed writeback. The iomap writeback error handling
code can clear the Uptodate flag if no portion of the page is
submitted for I/O. This is reproduced by fstest generic/019, which
combines various forms of I/O with simulated disk failures that
inevitably lead to filesystem shutdown (which then unconditionally
fails page writeback).

This is a regression introduced by commit f150b4234397 ("xfs: split
the iomap ops for buffered vs direct writes") due to the removal of
a shutdown check and explicit error return in the ->iomap_begin()
path used by the write fault path. The explicit error return
historically translated to a SIGBUS, but now carries on with iomap
processing where it complains about the unexpected state. Restore
the shutdown check to xfs_buffered_write_iomap_begin() to restore
historical behavior.

Fixes: f150b4234397 ("xfs: split the iomap ops for buffered vs direct writes")
Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/xfs/xfs_iomap.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 70c341658c01..6594f572096e 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -860,6 +860,9 @@ xfs_buffered_write_iomap_begin(
 	int			allocfork = XFS_DATA_FORK;
 	int			error = 0;
 
+	if (XFS_FORCED_SHUTDOWN(mp))
+		return -EIO;
+
 	/* we can't use delayed allocations when using extent size hints */
 	if (xfs_get_extsz_hint(ip))
 		return xfs_direct_write_iomap_begin(inode, offset, count,
-- 
2.26.2