On 4/18/25 10:06 PM, Ming Lei wrote: > Elevator switch code is another `nr_hw_queue` reader in non-fast-IO code > path, so it can't be done if updating `nr_hw_queues` is in-progress. > > Take same approach with not allowing add/del disk when updating > nr_hw_queues is in-progress, by holding srcu lock & check > set->updating_nr_hwq. > > Reported-by: Shinichiro Kawasaki <shinichiro.kawasaki@xxxxxxx> > Closes: https://lore.kernel.org/linux-block/mz4t4tlwiqjijw3zvqnjb7ovvvaegkqganegmmlc567tt5xj67@xal5ro544cnc/ > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> > --- > block/elevator.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/block/elevator.c b/block/elevator.c > index d25b9cc6c509..c23912652f96 100644 > --- a/block/elevator.c > +++ b/block/elevator.c > @@ -720,9 +720,10 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf, > { > char elevator_name[ELV_NAME_MAX]; > char *name; > - int ret; > + int ret, idx; > unsigned int memflags; > struct request_queue *q = disk->queue; > + struct blk_mq_tag_set *set = q->tag_set; > > /* > * If the attribute needs to load a module, do it before freezing the > @@ -734,6 +735,12 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf, > > elv_iosched_load_module(name); > > + idx = srcu_read_lock(&set->update_nr_hwq_srcu); > + if (set->updating_nr_hwq) { > + ret = -EBUSY; > + goto exit; > + } > + > memflags = blk_mq_freeze_queue(q); > mutex_lock(&q->elevator_lock); > ret = elevator_change(q, name); > @@ -741,6 +748,8 @@ ssize_t elv_iosched_store(struct gendisk *disk, const char *buf, > ret = count; > mutex_unlock(&q->elevator_lock); > blk_mq_unfreeze_queue(q, memflags); > +exit: > + srcu_read_unlock(&set->update_nr_hwq_srcu, idx); > return ret; > } > I have same comment here as well as I mentioned in the previous patch. (i.e. about using reader-writer lock instead of srcu). Thanks, --Nilay
