[PATCH 03/10] iomap: move locking out of iomap_write_delalloc_release

Christoph Hellwig
2024-09-23T15:29:20Z

XFS (which currently is the only user of iomap_write_delalloc_release)
already holds invalidate_lock for most zeroing operations. To be able
to avoid a deadlock it needs to stop taking the lock, but doing so
in iomap would leak XFS locking details into iomap.

To avoid this require the caller to hold invalidate_lock when calling
iomap_write_delalloc_release instead of taking it there.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/iomap/buffered-io.c | 17 ++++++++---------
fs/xfs/xfs_iomap.c | 2 ++
2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 237aeb883166df..232aaa1e86451a 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1211,12 +1211,13 @@ void iomap_write_delalloc_release(struct inode *inode, loff_t start_byte,
loff_t scan_end_byte = min(i_size_read(inode), end_byte);

/*
- * Lock the mapping to avoid races with page faults re-instantiating
- * folios and dirtying them via ->page_mkwrite whilst we walk the
- * cache and perform delalloc extent removal. Failing to do this can
- * leave dirty pages with no space reservation in the cache.
+ * The caller must hold invalidate_lock to avoid races with page faults
+ * re-instantiating folios and dirtying them via ->page_mkwrite whilst
+ * we walk the cache and perform delalloc extent removal. Failing to do
+ * this can leave dirty pages with no space reservation in the cache.
*/
- filemap_invalidate_lock(inode->i_mapping);
+ lockdep_assert_held_write(&inode->i_mapping->invalidate_lock);
+
while (start_byte < scan_end_byte) {
loff_t data_end;

@@ -1233,7 +1234,7 @@ void iomap_write_delalloc_release(struct inode *inode, loff_t start_byte,
if (start_byte == -ENXIO || start_byte == scan_end_byte)
break;
if (WARN_ON_ONCE(start_byte < 0))
- goto out_unlock;
+ return;
WARN_ON_ONCE(start_byte < punch_start_byte);
WARN_ON_ONCE(start_byte > scan_end_byte);

@@ -1244,7 +1245,7 @@ void iomap_write_delalloc_release(struct inode *inode, loff_t start_byte,
data_end = mapping_seek_hole_data(inode->i_mapping, start_byte,
scan_end_byte, SEEK_HOLE);
if (WARN_ON_ONCE(data_end < 0))
- goto out_unlock;
+ return;

/*
* If we race with post-direct I/O invalidation of the page cache,
@@ -1266,8 +1267,6 @@ void iomap_write_delalloc_release(struct inode *inode, loff_t start_byte,
if (punch_start_byte < end_byte)
punch(inode, punch_start_byte, end_byte - punch_start_byte,
iomap);
-out_unlock:
- filemap_invalidate_unlock(inode->i_mapping);
}
EXPORT_SYMBOL_GPL(iomap_write_delalloc_release);

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 30f2530b6d5461..01324da63fcfc7 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -1239,8 +1239,10 @@ xfs_buffered_write_iomap_end(
if (start_byte >= end_byte)
return 0;

+ filemap_invalidate_lock(inode->i_mapping);
iomap_write_delalloc_release(inode, start_byte, end_byte, flags, iomap,
xfs_buffered_write_delalloc_punch);
+ filemap_invalidate_unlock(inode->i_mapping);
return 0;
}

--
2.45.2