[PATCH 13/38] xfs: return -EAGAIN from xfs_reflink_allocate_cow for COW hole without transaction

When xfs_reflink_allocate_cow() encounters a COW fork hole that needs
a real extent allocated and no transaction has been provided, return
-EAGAIN to tell the caller to allocate a transaction and retry.

When a transaction is provided, pass it through to
xfs_reflink_fill_cow_hole() which will use it directly for the COW
extent allocation without needing to cycle the ILOCK.

This activates the retry loop added in the previous patch: on the
first call (tp == NULL), allocate_cow returns -EAGAIN, the caller
drops the ILOCK, allocates a transaction, and retries. On the
second call (tp != NULL), the transaction is passed down to
fill_cow_hole() and the COW allocation completes atomically
under the ILOCK without cycling it.

Assisted-by: LLM
Signed-off-by: Dave Chinner <[email protected]>
---
 fs/xfs/xfs_reflink.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 1ad0569ecdd1..56ad76b0f6b9 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -643,16 +643,22 @@ xfs_reflink_allocate_cow(
 
 	/*
 	 * CoW fork does not have an extent and data extent is shared.
-	 * Allocate a real extent in the CoW fork.
+	 * Allocate a real extent in the CoW fork. If the caller has not
+	 * provided a transaction for the allocation, return -EAGAIN to
+	 * tell the caller to allocate a transaction and retry.
 	 */
-	if (cmap->br_startoff > imap->br_startoff)
-		return xfs_reflink_fill_cow_hole(NULL, ip, imap, cmap, shared,
+	if (cmap->br_startoff > imap->br_startoff) {
+		if (!tp)
+			return -EAGAIN;
+		return xfs_reflink_fill_cow_hole(tp, ip, imap, cmap, shared,
 				lockmode, convert_now);
+	}
 
 	/*
 	 * CoW fork has a delalloc reservation. Replace it with a real extent.
 	 * There may or may not be a data fork mapping.
 	 */
+	ASSERT(!tp);
 	if (isnullstartblock(cmap->br_startblock) ||
 	    cmap->br_startblock == DELAYSTARTBLOCK)
 		return xfs_reflink_fill_delalloc(ip, imap, cmap, shared,
-- 
2.55.0