[PATCH 2/9] xfs: handle -EAGAIN from xfs_iomap_write_allocate

[Christoph Hellwig <hch@lst.de>]

-EAGAIN from xfs_iomap_write_allocate means that due to a racing
truncate there is no actual mapping at this offset anymore, and we
need to skip the block during writeback.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/xfs_aops.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 338b9d9984e0..da520860c85e 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -349,6 +349,7 @@ xfs_map_blocks(
 	imap_valid = offset_fsb >= wpc->imap.br_startoff &&
 		     offset_fsb < wpc->imap.br_startoff + wpc->imap.br_blockcount;
 	if (imap_valid &&
+	    !WARN_ON_ONCE(wpc->imap.br_startblock == HOLESTARTBLOCK) &&
 	    (!xfs_inode_has_cow_data(ip) ||
 	     wpc->io_type == XFS_IO_COW ||
 	     wpc->cow_seq == READ_ONCE(ip->i_cowfp->if_seq)))
@@ -454,8 +455,14 @@ xfs_map_blocks(
 allocate_blocks:
 	error = xfs_iomap_write_allocate(ip, whichfork, offset, &imap,
 			&wpc->cow_seq);
-	if (error)
+	if (error) {
+		if (error == -EAGAIN) {
+			/* we might have raced with truncate */
+			wpc->io_type = XFS_IO_HOLE;
+			error = 0;
+		}
 		return error;
+	}
 	ASSERT(whichfork == XFS_COW_FORK || cow_fsb == NULLFILEOFF ||
 	       imap.br_startoff + imap.br_blockcount <= cow_fsb);
 	wpc->imap = imap;
-- 
2.19.1