On Tue, Jan 23, 2018 at 04:57:34PM +0000, Bart Van Assche wrote: > On Wed, 2018-01-24 at 00:37 +0800, Ming Lei wrote: > > On Tue, Jan 23, 2018 at 04:24:20PM +0000, Bart Van Assche wrote: > > > My opinion about this patch is as follows: > > > * Changing a blk_mq_delay_run_hw_queue() call followed by return > > > BLK_STS_DEV_RESOURCE into return BLK_STS_RESOURCE is wrong because it changes > > > a guaranteed queue rerun into a queue rerun that may or may not happen > > > depending on whether or not multiple queue runs happen simultaneously. > > > > You may not understand the two: > > > > 1) it is always safe to return BLK_STS_RESOURCE, which will make sure to > > avoid IO hang by blk_mq_delay_run_hw_queue() or blk_mq_run_hw_queue(), > > and using which one depends on SCHED_RESTART. > > > > 2) if driver can make sure the queue will be rerun after some resource > > is available, either by itself or by blk-mq, it will return BLK_STS_DEV_RESOURCE > > > > So what is wrong with this way? > > Sorry, I swapped BLK_STS_DEV_RESOURCE and BLK_STS_RESOURCE accidentally in my > reply. What I meant is that changing a blk_mq_delay_run_hw_queue() call followed > by return BLK_STS_RESOURCE into BLK_STS_DEV_RESOURCE is wrong and introduces a > race condition in code where there was no race condition. OK, then no such race you worried about in this patch. Jens, could you take a look at this patch? Thanks, Ming
