On Wed, Aug 21, 2019 at 08:56:36AM -0700, Bart Van Assche wrote:
> On 8/21/19 2:15 AM, Ming Lei wrote:
> > blk_mq_realloc_hw_ctxs() is called from blk_mq_init_allocated_queue()
> > and blk_mq_update_nr_hw_queues(). For the former caller, the kobject
> > isn't exposed to userspace yet. For the latter caller, sysfs/debugfs
> > is un-registered before updating nr_hw_queues.
> >
> > On the other hand, commit 2f8f1336a48b ("blk-mq: always free hctx after
> > request queue is freed") moves freeing hctx into queue's release
> > handler, so there won't be race with queue release path too.
> >
> > So don't hold q->sysfs_lock in blk_mq_realloc_hw_ctxs().
>
> How about mentioning that the locking at the start of
> blk_mq_update_nr_hw_queues() serializes all blk_mq_realloc_hw_ctxs() calls
> that happen after a queue has been registered in sysfs?
This patch is actually wrong because elevator switch still may happen
during updating nr_hw_queues, since only hctx sysfs entries are
un-registered, and "queue/scheduler" is still visible to userspace.
So I will drop this patch in V3.
Thanks,
Ming
