On Mon, Sep 04, 2017 at 04:13:26AM +0000, Bart Van Assche wrote: > On Sat, 2017-09-02 at 21:12 +0800, Ming Lei wrote: > > Please let us know if V3 addresses your previous concern about calling > > blk_queue_enter_live() during preempt freezing. > > Do you understand how request queue cleanup works? The algorithm used for > request queue cleanup is as follows: > * Set the DYING flag. This flag makes all later blk_get_request() calls > fail. If you look at the __blk_freeze_queue_start(), you will see that preemp freeze will fail after queue is dying, and blk_queue_enter_live() won't be called at all if queue is dying, right? > * Wait until all pending requests have finished. > * Set the DEAD flag. For the traditional block layer, this flag causes > blk_run_queue() not to call .request_fn() anymore. For blk-mq it is > guaranteed in another way that .queue_rq() won't be called anymore after > this flag has been set. > > Allowing blk_get_request() to succeed after the DYING flag has been set is > completely wrong because that could result in a request being queued after See above, this patch changes nothing about this fact, please look at the patch carefully next time just before posting your long comment. > the DEAD flag has been set, resulting in either a hanging request or a kernel > crash. This is why it's completely wrong to add a blk_queue_enter_live() call > in blk_old_get_request() or blk_mq_alloc_request(). Hence my NAK for any > patch that adds a blk_queue_enter_live() call to any function called from > blk_get_request(). That includes the patch at the start of this e-mail thread. > > Bart. -- Ming
