xfs: xfs_log_force_lsn isn't passed a LSN

commit 5f9b4b0de8dc2fb8eb655463b438001c111570fe upstream.

[backported from CIL scalability series for dependency]

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>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/xfs/xfs_log.h

@@ -106,7 +106,7 @@ struct xfs_item_ops;
 struct xfs_trans;
 
 int	  xfs_log_force(struct xfs_mount *mp, uint flags);
-int	  xfs_log_force_lsn(struct xfs_mount *mp, xfs_lsn_t lsn, uint flags,
+int	  xfs_log_force_seq(struct xfs_mount *mp, xfs_csn_t seq, uint flags,
 		int *log_forced);
 int	  xfs_log_mount(struct xfs_mount	*mp,
 			struct xfs_buftarg	*log_target,
@@ -132,8 +132,6 @@ bool	xfs_log_writable(struct xfs_mount *mp);
 struct xlog_ticket *xfs_log_ticket_get(struct xlog_ticket *ticket);
 void	  xfs_log_ticket_put(struct xlog_ticket *ticket);
 
-void	xfs_log_commit_cil(struct xfs_mount *mp, struct xfs_trans *tp,
-				xfs_lsn_t *commit_lsn, bool regrant);
 void	xlog_cil_process_committed(struct list_head *list);
 bool	xfs_log_item_in_current_chkpt(struct xfs_log_item *lip);