Re: [PATCH 5/8] xfs: factor out log write ordering from xlog_cil_push_work()

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

On Thu, Jun 17, 2021 at 06:26:14PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> So we can use it for start record ordering as well as commit record
> ordering in future.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

This tricked me for a second until I realized that xlog_cil_order_write
is the chunk of code just prior to the xlog_cil_write_commit_record
call.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
>  fs/xfs/xfs_log_cil.c | 89 ++++++++++++++++++++++++++------------------
>  1 file changed, 52 insertions(+), 37 deletions(-)
> 
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index 35fc3e57d870..f993ec69fc97 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
> @@ -784,9 +784,54 @@ xlog_cil_build_trans_hdr(
>  }
>  
>  /*
> - * Write out the commit record of a checkpoint transaction associated with the
> - * given ticket to close off a running log write. Return the lsn of the commit
> - * record.
> + * Ensure that the order of log writes follows checkpoint sequence order. This
> + * relies on the context LSN being zero until the log write has guaranteed the
> + * LSN that the log write will start at via xlog_state_get_iclog_space().
> + */
> +static int
> +xlog_cil_order_write(
> +	struct xfs_cil		*cil,
> +	xfs_csn_t		sequence)
> +{
> +	struct xfs_cil_ctx	*ctx;
> +
> +restart:
> +	spin_lock(&cil->xc_push_lock);
> +	list_for_each_entry(ctx, &cil->xc_committing, committing) {
> +		/*
> +		 * Avoid getting stuck in this loop because we were woken by the
> +		 * shutdown, but then went back to sleep once already in the
> +		 * shutdown state.
> +		 */
> +		if (XLOG_FORCED_SHUTDOWN(cil->xc_log)) {
> +			spin_unlock(&cil->xc_push_lock);
> +			return -EIO;
> +		}
> +
> +		/*
> +		 * Higher sequences will wait for this one so skip them.
> +		 * Don't wait for our own sequence, either.
> +		 */
> +		if (ctx->sequence >= sequence)
> +			continue;
> +		if (!ctx->commit_lsn) {
> +			/*
> +			 * It is still being pushed! Wait for the push to
> +			 * complete, then start again from the beginning.
> +			 */
> +			xlog_wait(&cil->xc_commit_wait, &cil->xc_push_lock);
> +			goto restart;
> +		}
> +	}
> +	spin_unlock(&cil->xc_push_lock);
> +	return 0;
> +}
> +
> +/*
> + * Write out the commit record of a checkpoint transaction to close off a
> + * running log write. These commit records are strictly ordered in ascending CIL
> + * sequence order so that log recovery will always replay the checkpoints in the
> + * correct order.
>   */
>  int
>  xlog_cil_write_commit_record(
> @@ -816,6 +861,10 @@ xlog_cil_write_commit_record(
>  	if (XLOG_FORCED_SHUTDOWN(log))
>  		return -EIO;
>  
> +	error = xlog_cil_order_write(ctx->cil, ctx->sequence);
> +	if (error)
> +		return error;
> +
>  	/* account for space used by record data */
>  	ctx->ticket->t_curr_res -= reg.i_len;
>  	error = xlog_write(log, ctx, &lv_chain, ctx->ticket, iclog, reg.i_len);
> @@ -1048,40 +1097,6 @@ xlog_cil_push_work(
>  	if (error)
>  		goto out_abort_free_ticket;
>  
> -	/*
> -	 * now that we've written the checkpoint into the log, strictly
> -	 * order the commit records so replay will get them in the right order.
> -	 */
> -restart:
> -	spin_lock(&cil->xc_push_lock);
> -	list_for_each_entry(new_ctx, &cil->xc_committing, committing) {
> -		/*
> -		 * Avoid getting stuck in this loop because we were woken by the
> -		 * shutdown, but then went back to sleep once already in the
> -		 * shutdown state.
> -		 */
> -		if (XLOG_FORCED_SHUTDOWN(log)) {
> -			spin_unlock(&cil->xc_push_lock);
> -			goto out_abort_free_ticket;
> -		}
> -
> -		/*
> -		 * Higher sequences will wait for this one so skip them.
> -		 * Don't wait for our own sequence, either.
> -		 */
> -		if (new_ctx->sequence >= ctx->sequence)
> -			continue;
> -		if (!new_ctx->commit_lsn) {
> -			/*
> -			 * It is still being pushed! Wait for the push to
> -			 * complete, then start again from the beginning.
> -			 */
> -			xlog_wait(&cil->xc_commit_wait, &cil->xc_push_lock);
> -			goto restart;
> -		}
> -	}
> -	spin_unlock(&cil->xc_push_lock);
> -
>  	error = xlog_cil_write_commit_record(ctx, &commit_iclog);
>  	if (error)
>  		goto out_abort_free_ticket;
> -- 
> 2.31.1
>