On Thu, Sep 23, 2021 at 02:39:59PM +0800, Ming Lei wrote: > > > After blk_mq_unfreeze_queue() returns, blk_try_enter_queue() will return > > > true, so new FS I/O from opened bdev still won't be blocked, right? > > > > It won't be blocked by blk_mq_unfreeze_queue, but because the capacity > > is set to 0 it still won't make it to the driver. > > One bio could be made & checked before set_capacity(0), then is > submitted after blk_mq_unfreeze_queue() returns. > > blk_mq_freeze_queue_wait() doesn't always imply RCU grace period, for > example, the .q_usage_counter may have been in atomic mode before > calling blk_queue_start_drain() & blk_mq_freeze_queue_wait(). True, but this isn't really a new issue as we never had proper quiesce behavior. I have a bunch of ideas of how to make this actually solid, but none of them looks like 5.15 material.
