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

Dave Chinner
2021-06-22T04:06:13Z

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>
---
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