xfs: xfs_log_force_lsn isn't passed a LSN

In doing an investigation into AIL push stalls, I was looking at the
log force code to see if an async CIL push could be done instead.
This lead me to xfs_log_force_lsn() and looking at how it works.

xfs_log_force_lsn() is only called from inode synchronisation
contexts such as fsync(), and it takes the ip->i_itemp->ili_last_lsn
value as the LSN to sync the log to. This gets passed to
xlog_cil_force_lsn() via xfs_log_force_lsn() to flush the CIL to the
journal, and then used by xfs_log_force_lsn() to flush the iclogs to
the journal.

The problem is that ip->i_itemp->ili_last_lsn does not store a
log sequence number. What it stores is passed to it from the
->iop_committing method, which is called by xfs_log_commit_cil().
The value this passes to the iop_committing method is the CIL
context sequence number that the item was committed to.

As it turns out, xlog_cil_force_lsn() converts the sequence to an
actual commit LSN for the related context and returns that to
xfs_log_force_lsn(). xfs_log_force_lsn() overwrites it's "lsn"
variable that contained a sequence with an actual LSN and then uses
that to sync the iclogs.

This caused me some confusion for a while, even though I originally
wrote all this code a decade ago. ->iop_committing is only used by
a couple of log item types, and only inode items use the sequence
number it is passed.

Let's clean up the API, CIL structures and inode log item to call it
a sequence number, and make it clear that the high level code is
using CIL sequence numbers and not on-disk LSNs for integrity
synchronisation purposes.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 586f2992b789..87bffd12c20c 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -839,7 +839,7 @@ __xfs_trans_commit(
 	bool			regrant)
 {
 	struct xfs_mount	*mp = tp->t_mountp;
-	xfs_lsn_t		commit_lsn = -1;
+	xfs_csn_t		commit_seq = 0;
 	int			error = 0;
 	int			sync = tp->t_flags & XFS_TRANS_SYNC;
 
@@ -881,7 +881,7 @@ __xfs_trans_commit(
 		xfs_trans_apply_sb_deltas(tp);
 	xfs_trans_apply_dquot_deltas(tp);
 
-	xfs_log_commit_cil(mp, tp, &commit_lsn, regrant);
+	xlog_cil_commit(mp->m_log, tp, &commit_seq, regrant);
 
 	xfs_trans_free(tp);
 
@@ -890,7 +890,7 @@ __xfs_trans_commit(
 	 * log out now and wait for it.
 	 */
 	if (sync) {
-		error = xfs_log_force_lsn(mp, commit_lsn, XFS_LOG_SYNC, NULL);
+		error = xfs_log_force_seq(mp, commit_seq, XFS_LOG_SYNC, NULL);
 		XFS_STATS_INC(mp, xs_trans_sync);
 	} else {
 		XFS_STATS_INC(mp, xs_trans_async);