On Wed, Aug 14, 2019 at 1:34 PM Ming Lei <ming....@redhat.com> wrote: > Another candidate is to not switch to q_usage_counter's percpu mode > until loop becomes Lo_bound, and this way may be more clean.
Thanks! I had considered this too, but thought it a bit risky to mess with the init flag from the loop driver. Maybe we could delay switching q_usage_counter to per-cpu mode in the block layer in general, until the first request comes in? This would also address our issues, and potentially be an even smaller change. Martijn > > Something like the following patch: > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > index a7461f482467..8791f9242583 100644 > --- a/drivers/block/loop.c > +++ b/drivers/block/loop.c > @@ -1015,6 +1015,9 @@ static int loop_set_fd(struct loop_device *lo, fmode_t > mode, > */ > bdgrab(bdev); > mutex_unlock(&loop_ctl_mutex); > + > + percpu_ref_switch_to_percpu(&lo->lo_queue->q_usage_counter); > + > if (partscan) > loop_reread_partitions(lo, bdev); > if (claimed_bdev) > @@ -1171,6 +1174,8 @@ static int __loop_clr_fd(struct loop_device *lo, bool > release) > lo->lo_state = Lo_unbound; > mutex_unlock(&loop_ctl_mutex); > > + percpu_ref_switch_to_atomic(&lo->lo_queue->q_usage_counter, NULL); > + > /* > * Need not hold loop_ctl_mutex to fput backing file. > * Calling fput holding loop_ctl_mutex triggers a circular > @@ -2003,6 +2008,12 @@ static int loop_add(struct loop_device **l, int i) > } > lo->lo_queue->queuedata = lo; > > + /* > + * cheat block layer for not switching to q_usage_counter's > + * percpu mode before loop becomes Lo_bound > + */ > + blk_queue_flag_set(QUEUE_FLAG_INIT_DONE, lo->lo_queue); > + > blk_queue_max_hw_sectors(lo->lo_queue, BLK_DEF_MAX_SECTORS); > > /* > > > thanks, > Ming