RDMA/srp: Rework SCSI device reset handling

Since .scsi_done() must only be called after scsi_queue_rq() has
finished, make sure that the SRP initiator driver does not call
.scsi_done() while scsi_queue_rq() is in progress. Although
invoking sg_reset -d while I/O is in progress works fine with kernel
v4.20 and before, that is not the case with kernel v5.0-rc1. This
patch avoids that the following crash is triggered with kernel
v5.0-rc1:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000138
CPU: 0 PID: 360 Comm: kworker/0:1H Tainted: G    B             5.0.0-rc1-dbg+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
Workqueue: kblockd blk_mq_run_work_fn
RIP: 0010:blk_mq_dispatch_rq_list+0x116/0xb10
Call Trace:
 blk_mq_sched_dispatch_requests+0x2f7/0x300
 __blk_mq_run_hw_queue+0xd6/0x180
 blk_mq_run_work_fn+0x27/0x30
 process_one_work+0x4f1/0xa20
 worker_thread+0x67/0x5b0
 kthread+0x1cf/0x1f0
 ret_from_fork+0x24/0x30

Cc: <stable@vger.kernel.org>
Fixes: 94a9174c ("IB/srp: reduce lock coverage of command completion")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/ulp/srp/ib_srp.c

@@ -3032,7 +3032,6 @@ static int srp_reset_device(struct scsi_cmnd *scmnd)
 {
 	struct srp_target_port *target = host_to_target(scmnd->device->host);
 	struct srp_rdma_ch *ch;
-	int i, j;
 	u8 status;
 
 	shost_printk(KERN_ERR, target->scsi_host, "SRP reset_device called\n");
@@ -3044,15 +3043,6 @@ static int srp_reset_device(struct scsi_cmnd *scmnd)
 	if (status)
 		return FAILED;
 
-	for (i = 0; i < target->ch_count; i++) {
-		ch = &target->ch[i];
-		for (j = 0; j < target->req_ring_size; ++j) {
-			struct srp_request *req = &ch->req_ring[j];
-
-			srp_finish_req(ch, req, scmnd->device, DID_RESET << 16);
-		}
-	}
-
 	return SUCCESS;
 }