On Fri, 2017-04-07 at 17:46 +0800, Ming Lei wrote:
> On Thu, Apr 06, 2017 at 11:10:46AM -0700, Bart Van Assche wrote:
> > Since the next patch in this series will use RCU to iterate over
> > tag_list, make this safe. Add lockdep_assert_held() statements
> > in functions that iterate over tag_list to make clear that using
> > list_for_each_entry() instead of list_for_each_entry_rcu() is
> > fine in these functions.
> >
> > Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
> > Cc: Christoph Hellwig <hch@xxxxxx>
> > Cc: Hannes Reinecke <hare@xxxxxxxx>
> > ---
> > block/blk-mq.c | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index f7cd3208bcdf..b5580b09b4a5 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -2076,6 +2076,8 @@ static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set, bool shared)
> > {
> > struct request_queue *q;
> >
> > + lockdep_assert_held(&set->tag_list_lock);
> > +
> > list_for_each_entry(q, &set->tag_list, tag_set_list) {
> > blk_mq_freeze_queue(q);
> > queue_set_hctx_shared(q, shared);
> > @@ -2096,6 +2098,8 @@ static void blk_mq_del_queue_tag_set(struct request_queue *q)
> > blk_mq_update_tag_set_depth(set, false);
> > }
> > mutex_unlock(&set->tag_list_lock);
> > +
> > + synchronize_rcu();
>
> Looks synchronize_rcu() is only needed in deletion path, so it can
> be moved to blk_mq_del_queue_tag_set().
>
> Also list_del_init/list_add_tail() need to be replaced with RCU
> safe version in functions operating &set->tag_list.
Hello Ming,
I will replace list_del_init() / list_add_tail() by their RCU equivalents.
Regarding synchronize_rcu(): have you noticed that that call has been added to
blk_mq_del_queue_tag_set(), the function you requested to move that call to?
Bart.
