On 2020-08-27 13:33, Alan Stern wrote:
> It may not need to be that complicated. what about something like this?
>
> Index: usb-devel/block/blk-core.c
> ===================================================================
> --- usb-devel.orig/block/blk-core.c
> +++ usb-devel/block/blk-core.c
> @@ -420,11 +420,11 @@ EXPORT_SYMBOL(blk_cleanup_queue);
> /**
> * blk_queue_enter() - try to increase q->q_usage_counter
> * @q: request queue pointer
> - * @flags: BLK_MQ_REQ_NOWAIT and/or BLK_MQ_REQ_PREEMPT
> + * @flags: BLK_MQ_REQ_NOWAIT and/or BLK_MQ_REQ_PM
> */
> int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
> {
> - const bool pm = flags & BLK_MQ_REQ_PREEMPT;
> + const bool pm = flags & BLK_MQ_REQ_PM;
>
> while (true) {
> bool success = false;
> @@ -626,7 +626,8 @@ struct request *blk_get_request(struct r
> struct request *req;
>
> WARN_ON_ONCE(op & REQ_NOWAIT);
> - WARN_ON_ONCE(flags & ~(BLK_MQ_REQ_NOWAIT | BLK_MQ_REQ_PREEMPT));
> + WARN_ON_ONCE(flags & ~(BLK_MQ_REQ_NOWAIT | BLK_MQ_REQ_PREEMPT |
> + BLK_MQ_REQ_PM));
>
> req = blk_mq_alloc_request(q, op, flags);
> if (!IS_ERR(req) && q->mq_ops->initialize_rq_fn)
> Index: usb-devel/drivers/scsi/scsi_lib.c
> ===================================================================
> --- usb-devel.orig/drivers/scsi/scsi_lib.c
> +++ usb-devel/drivers/scsi/scsi_lib.c
> @@ -245,11 +245,15 @@ int __scsi_execute(struct scsi_device *s
> {
> struct request *req;
> struct scsi_request *rq;
> + blk_mq_req_flags_t mq_req_flags;
> int ret = DRIVER_ERROR << 24;
>
> + mq_req_flags = BLK_MQ_REQ_PREEMPT;
> + if (rq_flags & RQF_PM)
> + mq_req_flags |= BLK_MQ_REQ_PM;
> req = blk_get_request(sdev->request_queue,
> data_direction == DMA_TO_DEVICE ?
> - REQ_OP_SCSI_OUT : REQ_OP_SCSI_IN, BLK_MQ_REQ_PREEMPT);
> + REQ_OP_SCSI_OUT : REQ_OP_SCSI_IN, mq_req_flags);
> if (IS_ERR(req))
> return ret;
> rq = scsi_req(req);
> Index: usb-devel/include/linux/blk-mq.h
> ===================================================================
> --- usb-devel.orig/include/linux/blk-mq.h
> +++ usb-devel/include/linux/blk-mq.h
> @@ -435,6 +435,8 @@ enum {
> BLK_MQ_REQ_RESERVED = (__force blk_mq_req_flags_t)(1 << 1),
> /* set RQF_PREEMPT */
> BLK_MQ_REQ_PREEMPT = (__force blk_mq_req_flags_t)(1 << 3),
> + /* used for power management */
> + BLK_MQ_REQ_PM = (__force blk_mq_req_flags_t)(1 << 4),
> };
>
> struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
I think this patch will break SCSI domain validation. The SCSI domain
validation code calls scsi_device_quiesce() and that function in turn calls
blk_set_pm_only(). The SCSI domain validation code submits SCSI commands with
the BLK_MQ_REQ_PREEMPT flag. Since the above code postpones such requests
while blk_set_pm_only() is in effect, I think the above patch will cause the
SCSI domain validation code to deadlock.
Bart.
