zfs_log_write: only put the callback on the last itx

If a write is split across mutliple itxs, we only want the callback on
the last one, otherwise it will be called for every itx associated with
this single write, which makes it very hard to know what to clean up.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Mark Johnston <[email protected]>
Reviewed-by: Alexander Motin <[email protected]>
Signed-off-by: Rob Norris <[email protected]>
Closes #17445

Author: robn

module/zfs/zfs_log.c

@@ -693,8 +693,11 @@ zfs_log_write(zilog_t *zilog, dmu_tx_t *tx, int txtype,
 		itx->itx_sync = (zp->z_sync_cnt != 0);
 		itx->itx_gen = gen;
 
-		itx->itx_callback = callback;
-		itx->itx_callback_data = callback_data;
+		if (resid == len) {
+			itx->itx_callback = callback;
+			itx->itx_callback_data = callback_data;
+		}
+
 		zil_itx_assign(zilog, itx, tx);
 
 		off += len;