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. Bart.
