[PATCH 14/21] xfs: only run precommits once per transaction object

["Darrick J. Wong" <djwong@kernel.org>]

From: Darrick J. Wong <djwong@kernel.org>

Committing a transaction tx0 with a defer ops chain of (A, B, C)
creates a chain of transactions that looks like this:

tx0 -> txA -> txB -> txC

Prior to commit cb042117488dbf, __xfs_trans_commit would run precommits
on tx0, then call xfs_defer_finish_noroll to convert A-C to tx[A-C].
Unfortunately, after the finish_noroll loop we forgot to run precommits
on txC.  That was fixed by adding the second precommit call.

Unfortunately, none of us remembered that xfs_defer_finish_noroll
calls __xfs_trans_commit a second time to commit tx0 before finishing
work A in txA and committing that.  In other words, we run precommits
twice on tx0:

xfs_trans_commit(tx0)
    __xfs_trans_commit(tx0, false)
        xfs_trans_run_precommits(tx0)
        xfs_defer_finish_noroll(tx0)
            xfs_trans_roll(tx0)
                txA = xfs_trans_dup(tx0)
                __xfs_trans_commit(tx0, true)
                xfs_trans_run_precommits(tx0)

This currently isn't an issue because the inode item precommit is
idempotent; the iunlink item precommit deletes itself so it can't be
called again; and the buffer/dquot item precommits only check the incore
objects for corruption.  However, it doesn't make sense to run
precommits twice.

Fix this situation by only running precommits after finish_noroll.

Cc: <stable@vger.kernel.org> # v6.4
Fixes: cb042117488dbf ("xfs: defered work could create precommits")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
---
 fs/xfs/xfs_trans.c |   16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)


diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 05b18e30368e4b..4a517250efc911 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -860,13 +860,6 @@ __xfs_trans_commit(
 
 	trace_xfs_trans_commit(tp, _RET_IP_);
 
-	error = xfs_trans_run_precommits(tp);
-	if (error) {
-		if (tp->t_flags & XFS_TRANS_PERM_LOG_RES)
-			xfs_defer_cancel(tp);
-		goto out_unreserve;
-	}
-
 	/*
 	 * Finish deferred items on final commit. Only permanent transactions
 	 * should ever have deferred ops.
@@ -877,13 +870,12 @@ __xfs_trans_commit(
 		error = xfs_defer_finish_noroll(&tp);
 		if (error)
 			goto out_unreserve;
-
-		/* Run precommits from final tx in defer chain. */
-		error = xfs_trans_run_precommits(tp);
-		if (error)
-			goto out_unreserve;
 	}
 
+	error = xfs_trans_run_precommits(tp);
+	if (error)
+		goto out_unreserve;
+
 	/*
 	 * If there is nothing to be logged by the transaction,
 	 * then unlock all of the items associated with the