[PATCH v3 2/6] ntfs: do not turn an unmappable runlist fragment into delalloc on write

[Matthias Goergens]

ntfs_write_simple_iomap_begin_non_resident() has the same unchecked
retry.  LCN_RL_NOT_MAPPED passes its "lcn <= LCN_HOLE" test, so a
buffered write into a range whose extent record cannot be read is
merged into the runlist as LCN_DELALLOC over clusters that are already
allocated on disk, and write() succeeds.  If the record stays
unreadable, writeback fails too and the data never reaches the disk;
the error only shows up at a later fsync() or a synchronous write.

On the volume from the previous patch, after a read of the file, an
8 KiB pwrite() at vcn 1000 returns 8192, fsync() returns -EIO, and
after remount the range is unchanged.

Fail the lookup here too, with -ENOMEM or -EIO.  That pwrite() now
fails with -EIO.  Writes whose range can be mapped are unaffected.

Fixes: b041ca562526 ("ntfs: update iomap and address space operations")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Matthias Goergens <matthias.goergens@xxxxxxxxx>
---
 fs/ntfs/iomap.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/fs/ntfs/iomap.c b/fs/ntfs/iomap.c
index c812d7f19b360..b4475963e57a7 100644
--- a/fs/ntfs/iomap.c
+++ b/fs/ntfs/iomap.c
@@ -394,7 +394,7 @@ static int ntfs_write_simple_iomap_begin_non_resident(struct inode *inode, loff_
 	loff_t vcn_ofs, rl_length;
 	struct runlist_element *rl, *rlc;
 	bool is_retry = false;
-	int err = 0;
+	int err = 0, map_err = 0;
 	s64 vcn, lcn;
 	s64 max_clu_count =
 		ntfs_bytes_to_cluster(vol, round_up(length, vol->cluster_size));
@@ -429,12 +429,24 @@ static int ntfs_write_simple_iomap_begin_non_resident(struct inode *inode, loff_
 
 	if (lcn <= LCN_RL_NOT_MAPPED && is_retry == false) {
 		is_retry = true;
-		if (!ntfs_map_runlist_nolock(ni, vcn, NULL)) {
+		map_err = ntfs_map_runlist_nolock(ni, vcn, NULL);
+		if (!map_err) {
 			rl = ni->runlist.rl;
 			goto remap_rl;
 		}
 	}
 
+	/*
+	 * As in ntfs_attr_vcn_to_rl(): a runlist fragment that could not be
+	 * mapped is not a hole.  Treating it as one would put a delalloc
+	 * extent over clusters that are allocated on disk but unknown to us.
+	 */
+	if (lcn == LCN_RL_NOT_MAPPED) {
+		up_write(&ni->runlist.lock);
+		mutex_unlock(&ni->mrec_lock);
+		return map_err == -ENOMEM ? -ENOMEM : -EIO;
+	}
+
 	max_clu_count = min(max_clu_count, rl->length - (vcn - rl->vcn));
 	if (max_clu_count == 0) {
 		ntfs_error(inode->i_sb,
-- 
2.55.0