[PATCH 16/33] xfs: use rolling transaction in xfs_bmapi_convert_delalloc

Move the transaction allocation, ILOCK acquisition and inode join
up from xfs_bmapi_convert_one_delalloc() into
xfs_bmapi_convert_delalloc(). Pass the transaction down to each
call to xfs_bmapi_convert_one_delalloc(), and use xfs_defer_finish()
after each iteration to process deferred operations and roll the
transaction while keeping the ILOCK held.

The rolling transaction keeps the ILOCK held across the entire
conversion loop, making this multi-extent conversion operation
atomic with respect to other concurrent extent operations.

Assisted-by: LLM
Signed-off-by: Dave Chinner <[email protected]>
---
 fs/xfs/libxfs/xfs_bmap.c | 35 ++++++++++++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 7f3a3a02a035..4eaf67b51c8d 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -4503,8 +4503,26 @@ xfs_bmapi_convert_delalloc(
 	struct iomap		*iomap,
 	unsigned int		*seq)
 {
+	struct xfs_mount	*mp = ip->i_mount;
+	struct xfs_trans	*tp;
 	int			error;
 
+	/*
+	 * Allocate the transaction, take the ILOCK and join the inode to it.
+	 * Space for the extent and indirect blocks was reserved when the
+	 * delalloc extent was created so there's no need to reserve blocks.
+	 * The rolling transaction keeps the ILOCK held across the entire
+	 * conversion loop, making this multi-extent conversion operation
+	 * atomic with respect to other concurrent extent operations.
+	 */
+	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, 0, 0,
+				XFS_TRANS_RESERVE, &tp);
+	if (error)
+		return error;
+
+	xfs_ilock(ip, XFS_ILOCK_EXCL);
+	xfs_trans_ijoin(tp, ip, 0);
+
 	/*
 	 * Attempt to allocate whatever delalloc extent currently backs offset
 	 * and put the result into iomap.  Allocate in a loop because it may
@@ -4512,13 +4530,24 @@ xfs_bmapi_convert_delalloc(
 	 * delalloc extent if free space is sufficiently fragmented.
 	 */
 	do {
-		error = xfs_bmapi_convert_one_delalloc(NULL, ip, whichfork,
+		error = xfs_bmapi_convert_one_delalloc(tp, ip, whichfork,
 					offset, iomap, seq);
 		if (error)
-			return error;
+			goto out_trans_cancel;
+
+		error = xfs_defer_finish(&tp);
+		if (error)
+			goto out_trans_cancel;
 	} while (iomap->offset + iomap->length <= offset);
 
-	return 0;
+	error = xfs_trans_commit(tp);
+	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+	return error;
+
+out_trans_cancel:
+	xfs_trans_cancel(tp);
+	xfs_iunlock(ip, XFS_ILOCK_EXCL);
+	return error;
 }
 
 int
-- 
2.55.0