xfs: attach iclog callbacks in xlog_cil_set_ctx_write_state()

Now that we have a mechanism to guarantee that the callbacks
attached to an iclog are owned by the context that attaches them
until they drop their reference to the iclog via
xlog_state_release_iclog(), we can attach callbacks to the iclog at
any time we have an active reference to the iclog.

xlog_state_get_iclog_space() always guarantees that the commit
record will fit in the iclog it returns, so we can move this IO
callback setting to xlog_cil_set_ctx_write_state(), record the
commit iclog in the context and remove the need for the commit iclog
to be returned by xlog_write() altogether.

This, in turn, allows us to move the wakeup for ordered commit
record writes up into xlog_cil_set_ctx_write_state(), too, because
we have been guaranteed that this commit record will be physically
located in the iclog before any waiting commit record at a higher
sequence number will be granted iclog space.

This further cleans up the post commit record write processing in
the CIL push code, especially as xlog_state_release_iclog() will now
clean up the context when shutdown errors occur.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

fs/xfs/xfs_log.c

@@ -933,7 +933,7 @@ xlog_write_unmount_record(
 	/* account for space used by record data */
 	ticket->t_curr_res -= sizeof(ulf);
 
-	return xlog_write(log, NULL, &vec, ticket, NULL, XLOG_UNMOUNT_TRANS);
+	return xlog_write(log, NULL, &vec, ticket, XLOG_UNMOUNT_TRANS);
 }
 
 /*
@@ -2380,8 +2380,7 @@ xlog_write_copy_finish(
 	int			*data_cnt,
 	int			*partial_copy,
 	int			*partial_copy_len,
-	int			log_offset,
-	struct xlog_in_core	**commit_iclog)
+	int			log_offset)
 {
 	int			error;
 
@@ -2400,27 +2399,20 @@ xlog_write_copy_finish(
 	*partial_copy = 0;
 	*partial_copy_len = 0;
 
-	if (iclog->ic_size - log_offset <= sizeof(xlog_op_header_t)) {
-		/* no more space in this iclog - push it. */
-		spin_lock(&log->l_icloglock);
-		xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
-		*record_cnt = 0;
-		*data_cnt = 0;
-
-		if (iclog->ic_state == XLOG_STATE_ACTIVE)
-			xlog_state_switch_iclogs(log, iclog, 0);
-		else
-			ASSERT(iclog->ic_state == XLOG_STATE_WANT_SYNC ||
-				xlog_is_shutdown(log));
-		if (!commit_iclog)
-			goto release_iclog;
-		spin_unlock(&log->l_icloglock);
-		ASSERT(flags & XLOG_COMMIT_TRANS);
-		*commit_iclog = iclog;
-	}
+	if (iclog->ic_size - log_offset > sizeof(xlog_op_header_t))
+		return 0;
 
-	return 0;
+	/* no more space in this iclog - push it. */
+	spin_lock(&log->l_icloglock);
+	xlog_state_finish_copy(log, iclog, *record_cnt, *data_cnt);
+	*record_cnt = 0;
+	*data_cnt = 0;
 
+	if (iclog->ic_state == XLOG_STATE_ACTIVE)
+		xlog_state_switch_iclogs(log, iclog, 0);
+	else
+		ASSERT(iclog->ic_state == XLOG_STATE_WANT_SYNC ||
+			xlog_is_shutdown(log));
 release_iclog:
 	error = xlog_state_release_iclog(log, iclog, 0);
 	spin_unlock(&log->l_icloglock);
@@ -2473,7 +2465,6 @@ xlog_write(
 	struct xfs_cil_ctx	*ctx,
 	struct xfs_log_vec	*log_vector,
 	struct xlog_ticket	*ticket,
-	struct xlog_in_core	**commit_iclog,
 	uint			optype)
 {
 	struct xlog_in_core	*iclog = NULL;
@@ -2602,8 +2593,7 @@ xlog_write(
 						       &record_cnt, &data_cnt,
 						       &partial_copy,
 						       &partial_copy_len,
-						       log_offset,
-						       commit_iclog);
+						       log_offset);
 			if (error)
 				return error;
 
@@ -2641,12 +2631,7 @@ xlog_write(
 
 	spin_lock(&log->l_icloglock);
 	xlog_state_finish_copy(log, iclog, record_cnt, data_cnt);
-	if (commit_iclog) {
-		ASSERT(optype & XLOG_COMMIT_TRANS);
-		*commit_iclog = iclog;
-	} else {
-		error = xlog_state_release_iclog(log, iclog, 0);
-	}
+	error = xlog_state_release_iclog(log, iclog, 0);
 	spin_unlock(&log->l_icloglock);
 
 	return error;

fs/xfs/xfs_log_cil.c

@@ -646,11 +646,41 @@ xlog_cil_set_ctx_write_state(
 	xfs_lsn_t		lsn = be64_to_cpu(iclog->ic_header.h_lsn);
 
 	ASSERT(!ctx->commit_lsn);
-	spin_lock(&cil->xc_push_lock);
-	if (!ctx->start_lsn)
+	if (!ctx->start_lsn) {
+		spin_lock(&cil->xc_push_lock);
 		ctx->start_lsn = lsn;
-	else
-		ctx->commit_lsn = lsn;
+		spin_unlock(&cil->xc_push_lock);
+		return;
+	}
+
+	/*
+	 * Take a reference to the iclog for the context so that we still hold
+	 * it when xlog_write is done and has released it. This means the
+	 * context controls when the iclog is released for IO.
+	 */
+	atomic_inc(&iclog->ic_refcnt);
+
+	/*
+	 * xlog_state_get_iclog_space() guarantees there is enough space in the
+	 * iclog for an entire commit record, so we can attach the context
+	 * callbacks now.  This needs to be done before we make the commit_lsn
+	 * visible to waiters so that checkpoints with commit records in the
+	 * same iclog order their IO completion callbacks in the same order that
+	 * the commit records appear in the iclog.
+	 */
+	spin_lock(&cil->xc_log->l_icloglock);
+	list_add_tail(&ctx->iclog_entry, &iclog->ic_callbacks);
+	spin_unlock(&cil->xc_log->l_icloglock);
+
+	/*
+	 * Now we can record the commit LSN and wake anyone waiting for this
+	 * sequence to have the ordered commit record assigned to a physical
+	 * location in the log.
+	 */
+	spin_lock(&cil->xc_push_lock);
+	ctx->commit_iclog = iclog;
+	ctx->commit_lsn = lsn;
+	wake_up_all(&cil->xc_commit_wait);
 	spin_unlock(&cil->xc_push_lock);
 }
 
@@ -707,8 +737,7 @@ xlog_cil_order_write(
  */
 static int
 xlog_cil_write_commit_record(
-	struct xfs_cil_ctx	*ctx,
-	struct xlog_in_core	**iclog)
+	struct xfs_cil_ctx	*ctx)
 {
 	struct xlog		*log = ctx->cil->xc_log;
 	struct xfs_log_iovec	reg = {
@@ -725,8 +754,7 @@ xlog_cil_write_commit_record(
 	if (xlog_is_shutdown(log))
 		return -EIO;
 
-	error = xlog_write(log, ctx, &vec, ctx->ticket, iclog,
-			XLOG_COMMIT_TRANS);
+	error = xlog_write(log, ctx, &vec, ctx->ticket, XLOG_COMMIT_TRANS);
 	if (error)
 		xfs_force_shutdown(log->l_mp, SHUTDOWN_LOG_IO_ERROR);
 	return error;
@@ -756,7 +784,6 @@ xlog_cil_push_work(
 	struct xfs_log_vec	*lv;
 	struct xfs_cil_ctx	*ctx;
 	struct xfs_cil_ctx	*new_ctx;
-	struct xlog_in_core	*commit_iclog;
 	struct xlog_ticket	*tic;
 	int			num_iovecs;
 	int			error = 0;
@@ -945,44 +972,20 @@ xlog_cil_push_work(
 	 */
 	wait_for_completion(&bdev_flush);
 
-	error = xlog_write(log, ctx, &lvhdr, tic, NULL, XLOG_START_TRANS);
+	error = xlog_write(log, ctx, &lvhdr, tic, XLOG_START_TRANS);
 	if (error)
 		goto out_abort_free_ticket;
 
 	error = xlog_cil_order_write(ctx->cil, ctx->sequence);
 	if (error)
 		goto out_abort_free_ticket;
 
-	error = xlog_cil_write_commit_record(ctx, &commit_iclog);
+	error = xlog_cil_write_commit_record(ctx);
 	if (error)
 		goto out_abort_free_ticket;
 
 	xfs_log_ticket_ungrant(log, tic);
 
-	/*
-	 * Once we attach the ctx to the iclog, it is effectively owned by the
-	 * iclog and we can only use it while we still have an active reference
-	 * to the iclog. i.e. once we call xlog_state_release_iclog() we can no
-	 * longer safely reference the ctx.
-	 */
-	spin_lock(&log->l_icloglock);
-	if (xlog_is_shutdown(log)) {
-		spin_unlock(&log->l_icloglock);
-		goto out_abort;
-	}
-	ASSERT_ALWAYS(commit_iclog->ic_state == XLOG_STATE_ACTIVE ||
-		      commit_iclog->ic_state == XLOG_STATE_WANT_SYNC);
-	list_add_tail(&ctx->iclog_entry, &commit_iclog->ic_callbacks);
-
-	/*
-	 * now the checkpoint commit is complete and we've attached the
-	 * callbacks to the iclog we can assign the commit LSN to the context
-	 * and wake up anyone who is waiting for the commit to complete.
-	 */
-	spin_lock(&cil->xc_push_lock);
-	wake_up_all(&cil->xc_commit_wait);
-	spin_unlock(&cil->xc_push_lock);
-
 	/*
 	 * If the checkpoint spans multiple iclogs, wait for all previous iclogs
 	 * to complete before we submit the commit_iclog. We can't use state
@@ -995,34 +998,35 @@ xlog_cil_push_work(
 	 * iclog header lsn and compare it to the commit lsn to determine if we
 	 * need to wait on iclogs or not.
 	 */
+	spin_lock(&log->l_icloglock);
 	if (ctx->start_lsn != ctx->commit_lsn) {
 		xfs_lsn_t	plsn;
 
-		plsn = be64_to_cpu(commit_iclog->ic_prev->ic_header.h_lsn);
+		plsn = be64_to_cpu(ctx->commit_iclog->ic_prev->ic_header.h_lsn);
 		if (plsn && XFS_LSN_CMP(plsn, ctx->commit_lsn) < 0) {
 			/*
 			 * Waiting on ic_force_wait orders the completion of
 			 * iclogs older than ic_prev. Hence we only need to wait
 			 * on the most recent older iclog here.
 			 */
-			xlog_wait_on_iclog(commit_iclog->ic_prev);
+			xlog_wait_on_iclog(ctx->commit_iclog->ic_prev);
 			spin_lock(&log->l_icloglock);
 		}
 
 		/*
 		 * We need to issue a pre-flush so that the ordering for this
 		 * checkpoint is correctly preserved down to stable storage.
 		 */
-		commit_iclog->ic_flags |= XLOG_ICL_NEED_FLUSH;
+		ctx->commit_iclog->ic_flags |= XLOG_ICL_NEED_FLUSH;
 	}
 
 	/*
 	 * The commit iclog must be written to stable storage to guarantee
 	 * journal IO vs metadata writeback IO is correctly ordered on stable
 	 * storage.
 	 */
-	commit_iclog->ic_flags |= XLOG_ICL_NEED_FUA;
-	xlog_state_release_iclog(log, commit_iclog, preflush_tail_lsn);
+	ctx->commit_iclog->ic_flags |= XLOG_ICL_NEED_FUA;
+	xlog_state_release_iclog(log, ctx->commit_iclog, preflush_tail_lsn);
 
 	/* Not safe to reference ctx now! */
 
@@ -1037,9 +1041,15 @@ xlog_cil_push_work(
 
 out_abort_free_ticket:
 	xfs_log_ticket_ungrant(log, tic);
-out_abort:
 	ASSERT(xlog_is_shutdown(log));
-	xlog_cil_committed(ctx);
+	if (!ctx->commit_iclog) {
+		xlog_cil_committed(ctx);
+		return;
+	}
+	spin_lock(&log->l_icloglock);
+	xlog_state_release_iclog(log, ctx->commit_iclog, 0);
+	/* Not safe to reference ctx now! */
+	spin_unlock(&log->l_icloglock);
 }
 
 /*

fs/xfs/xfs_log_priv.h

@@ -240,6 +240,7 @@ struct xfs_cil_ctx {
 	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_in_core	*commit_iclog;
 	struct xlog_ticket	*ticket;	/* chkpt ticket */
 	int			nvecs;		/* number of regions */
 	int			space_used;	/* aggregate size of regions */
@@ -514,7 +515,7 @@ void	xlog_print_tic_res(struct xfs_mount *mp, struct xlog_ticket *ticket);
 void	xlog_print_trans(struct xfs_trans *);
 int	xlog_write(struct xlog *log, struct xfs_cil_ctx *ctx,
 		struct xfs_log_vec *log_vector, struct xlog_ticket *tic,
-		struct xlog_in_core **commit_iclog, uint optype);
+		uint optype);
 void	xfs_log_ticket_ungrant(struct xlog *log, struct xlog_ticket *ticket);
 void	xfs_log_ticket_regrant(struct xlog *log, struct xlog_ticket *ticket);