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, 7 insertions, 8 deletions

diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
index 2203ccecafb6..2d7e7cbee8b7 100644
--- a/fs/xfs/xfs_log_priv.h
+++ b/fs/xfs/xfs_log_priv.h
@@ -234,7 +234,7 @@ struct xfs_cil;
 
 struct xfs_cil_ctx {
 	struct xfs_cil		*cil;
-	xfs_lsn_t		sequence;	/* chkpt sequence # */
+	xfs_csn_t		sequence;	/* chkpt sequence # */
 	xfs_lsn_t		start_lsn;	/* first LSN of chkpt commit */
 	xfs_lsn_t		commit_lsn;	/* chkpt commit record lsn */
 	struct xlog_ticket	*ticket;	/* chkpt ticket */
@@ -272,10 +272,10 @@ struct xfs_cil {
 	struct xfs_cil_ctx	*xc_ctx;
 
 	spinlock_t		xc_push_lock ____cacheline_aligned_in_smp;
-	xfs_lsn_t		xc_push_seq;
+	xfs_csn_t		xc_push_seq;
 	struct list_head	xc_committing;
 	wait_queue_head_t	xc_commit_wait;
-	xfs_lsn_t		xc_current_sequence;
+	xfs_csn_t		xc_current_sequence;
 	struct work_struct	xc_push_work;
 	wait_queue_head_t	xc_push_wait;	/* background push throttle */
 } ____cacheline_aligned_in_smp;
@@ -554,19 +554,18 @@ int	xlog_cil_init(struct xlog *log);
 void	xlog_cil_init_post_recovery(struct xlog *log);
 void	xlog_cil_destroy(struct xlog *log);
 bool	xlog_cil_empty(struct xlog *log);
+void	xlog_cil_commit(struct xlog *log, struct xfs_trans *tp,
+			xfs_csn_t *commit_seq, bool regrant);
 
 /*
  * CIL force routines
  */
-xfs_lsn_t
-xlog_cil_force_lsn(
-	struct xlog *log,
-	xfs_lsn_t sequence);
+xfs_lsn_t xlog_cil_force_seq(struct xlog *log, xfs_csn_t sequence);
 
 static inline void
 xlog_cil_force(struct xlog *log)
 {
-	xlog_cil_force_lsn(log, log->l_cilp->xc_current_sequence);
+	xlog_cil_force_seq(log, log->l_cilp->xc_current_sequence);
 }
 
 /*