On Thu, Sep 03, 2020 at 08:35:45AM +0800, Ming Lei wrote:
> On Wed, Sep 02, 2020 at 11:52:59AM -0600, Jens Axboe wrote:
> > On 9/1/20 9:11 PM, Ming Lei wrote:
> > > On Tue, Aug 25, 2020 at 10:17:32PM +0800, Ming Lei wrote:
> > >> Hi Jens,
> > >>
> > >> The 1st patch add .mq_quiesce_mutex for serializing quiesce/unquiesce,
> > >> and prepares for replacing srcu with percpu_ref.
> > >>
> > >> The 2nd patch replaces srcu with percpu_ref.
> > >>
> > >> V2:
> > >> - add .mq_quiesce_lock
> > >> - add comment on patch 2 wrt. handling hctx_lock() failure
> > >> - trivial patch style change
> > >>
> > >>
> > >> Ming Lei (2):
> > >> blk-mq: serialize queue quiesce and unquiesce by mutex
> > >> blk-mq: implement queue quiesce via percpu_ref for BLK_MQ_F_BLOCKING
> > >>
> > >> block/blk-core.c | 2 +
> > >> block/blk-mq-sysfs.c | 2 -
> > >> block/blk-mq.c | 125 +++++++++++++++++++++++------------------
> > >> block/blk-sysfs.c | 6 +-
> > >> include/linux/blk-mq.h | 7 ---
> > >> include/linux/blkdev.h | 6 ++
> > >> 6 files changed, 82 insertions(+), 66 deletions(-)
> > >>
> > >> Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
> > >> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> > >> Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
> > >> Cc: Sagi Grimberg <sagi@xxxxxxxxxxx>
> > >> Cc: Bart Van Assche <bvanassche@xxxxxxx>
> > >> Cc: Johannes Thumshirn <Johannes.Thumshirn@xxxxxxx>
> > >> Cc: Chao Leng <lengchao@xxxxxxxxxx>
> > >> Cc: Christoph Hellwig <hch@xxxxxx>
> > >
> > > Hello Guys,
> > >
> > > Is there any objections on the two patches? If not, I'd suggest to move> on.
> >
> > Seems like the nested case is one that should either be handled, or at
> > least detected.
>
> Yeah, the 1st patch adds mutex for handling nested case correctly and efficiently.
That doesn't really do anything about handling nested quiesce/unquiesce.
It just prevents two threads from doing it at the same time, but anyone
can still undo the other's expected queue state. The following on top of
your series will at least detect the condition:
---
diff --git a/block/blk-mq.c b/block/blk-mq.c
index ef6c6fa8dab0..52b53f2bb567 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -249,6 +249,7 @@ void blk_mq_unquiesce_queue(struct request_queue *q)
{
mutex_lock(&q->mq_quiesce_lock);
+ WARN_ON(!blk_queue_quiesced(q));
blk_queue_flag_clear(QUEUE_FLAG_QUIESCED, q);
if (q->tag_set->flags & BLK_MQ_F_BLOCKING)
--
