On 9/5/21 2:51 AM, Adrian Hunter wrote:
There is no guarantee to be able to enter the queue if requests are blocked. That is because freezing the queue will block entry to the queue, but freezing also waits for outstanding requests which can make no progress while the queue is blocked. That situation can happen when the error handler issues requests to clear unit attention condition. Requests can be blocked if the ufshcd_state is UFSHCD_STATE_EH_SCHEDULED_FATAL, which can happen as a result either of error handler activity, or theoretically a request that is issued after the error handler unblocks the queue but before clearing unit attention condition. The deadlock is very unlikely, so the error handler can be expected to clear ua at some point anyway, so the simple solution is not to wait to enter the queue.
Do you agree that the interaction between ufshcd_scsi_block_requests() and blk_mq_freeze_queue() can only lead to a deadlock if blk_queue_enter() is called without using the BLK_MQ_REQ_NOWAIT flag and if unblocking SCSI request processing can only happen by the same thread? Do you agree that no ufshcd_clear_ua_wluns() caller blocks SCSI request processing and hence that it is not necessary to add a "nowait" argument to ufshcd_clear_ua_wluns()? Thanks, Bart.
