Re: [PATCH 2/4] xfs: remove callback dequeue loop from xlog_state_do_iclog_callbacks

Darrick J. Wong
2021-06-25T20:57:40Z

On Tue, Jun 22, 2021 at 02:06:02PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> If we are processing callbacks on an iclog, nothing can be
> concurrently adding callbacks to the loop. We only add callbacks to
> the iclog when they are in ACTIVE or WANT_SYNC state, and we
> explicitly do not add callbacks if the iclog is already in IOERROR
> state.
>
> The only way to have a dequeue racing with an enqueue is to be
> processing a shutdown without a direct reference to an iclog in
> ACTIVE or WANT_SYNC state. As the enqueue avoids this race
> condition, we only ever need a single dequeue operation in
> xlog_state_do_iclog_callbacks(). Hence we can remove the loop.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

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

--D

> ---
> fs/xfs/xfs_log.c | 16 ++++++----------
> 1 file changed, 6 insertions(+), 10 deletions(-)
>
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index bb4390942275..05b00fa4d661 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -2774,19 +2774,15 @@ xlog_state_do_iclog_callbacks(
> struct xlog *log,
> struct xlog_in_core *iclog)
> {
> - trace_xlog_iclog_callbacks_start(iclog, _RET_IP_);
> - spin_lock(&iclog->ic_callback_lock);
> - while (!list_empty(&iclog->ic_callbacks)) {
> - LIST_HEAD(tmp);
> + LIST_HEAD(tmp);
>
> - list_splice_init(&iclog->ic_callbacks, &tmp);
> -
> - spin_unlock(&iclog->ic_callback_lock);
> - xlog_cil_process_committed(&tmp);
> - spin_lock(&iclog->ic_callback_lock);
> - }
> + trace_xlog_iclog_callbacks_start(iclog, _RET_IP_);
>
> + spin_lock(&iclog->ic_callback_lock);
> + list_splice_init(&iclog->ic_callbacks, &tmp);
> spin_unlock(&iclog->ic_callback_lock);
> +
> + xlog_cil_process_committed(&tmp);
> trace_xlog_iclog_callbacks_done(iclog, _RET_IP_);
> }
>
> --
> 2.31.1
>