linux-kernel - Re: [RFC PATCH] blk-mq: fixup RESTART when queue becomes idle

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Message-ID: <1516316102.2676.97.camel@wdc.com>
Date:   Thu, 18 Jan 2018 22:55:03 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "snitzer@...hat.com" <snitzer@...hat.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "loberman@...hat.com" <loberman@...hat.com>
CC:     "dm-devel@...hat.com" <dm-devel@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hch@...radead.org" <hch@...radead.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "osandov@...com" <osandov@...com>,
        "ming.lei@...hat.com" <ming.lei@...hat.com>
Subject: Re: [RFC PATCH] blk-mq: fixup RESTART when queue becomes idle

On Thu, 2018-01-18 at 15:39 -0700, Jens Axboe wrote:
> When you do have a solid test case, please please submit a blktests
> test case for it! This needs to be something we can regularly in
> testing.

Hello Jens,

That sounds like a good idea to me. BTW, I think the reason why so far I
can reproduce these queue stalls easier than others is because I modified the
SRP initiator to make it easy to cause the .get_budget() call to succeed and
the scsi_queue_rq() to return BLK_STS_BUSY. A possible next step is to apply
a similar change to the scsi_debug driver. The change I made is as follows:

diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
index 0c887ebfbc64..7f3c4a197425 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.c
+++ b/drivers/infiniband/ulp/srp/ib_srp.c
@@ -3135,6 +3135,16 @@ static int srp_reset_host(struct scsi_cmnd *scmnd)
 	return srp_reconnect_rport(target->rport) == 0 ? SUCCESS : FAILED;
 }
 
+static int srp_target_alloc(struct scsi_target *starget)
+{
+	struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
+	struct srp_target_port *target = host_to_target(shost);
+
+	if (target->target_can_queue)
+		starget->can_queue = target->target_can_queue;
+	return 0;
+}
+
 static int srp_slave_alloc(struct scsi_device *sdev)
 {
 	struct Scsi_Host *shost = sdev->host;
@@ -3348,6 +3358,7 @@ static struct scsi_host_template srp_template = {
 	.module				= THIS_MODULE,
 	.name				= "InfiniBand SRP initiator",
 	.proc_name			= DRV_NAME,
+	.target_alloc			= srp_target_alloc,
 	.slave_alloc			= srp_slave_alloc,
 	.slave_configure		= srp_slave_configure,
 	.info				= srp_target_info,
@@ -3515,6 +3526,7 @@ enum {
 	SRP_OPT_QUEUE_SIZE	= 1 << 14,
 	SRP_OPT_IP_SRC		= 1 << 15,
 	SRP_OPT_IP_DEST		= 1 << 16,
+	SRP_OPT_TARGET_CAN_QUEUE= 1 << 17,
 };
 
 static unsigned int srp_opt_mandatory[] = {
@@ -3536,6 +3548,7 @@ static const match_table_t srp_opt_tokens = {
 	{ SRP_OPT_SERVICE_ID,		"service_id=%s"		},
 	{ SRP_OPT_MAX_SECT,		"max_sect=%d" 		},
 	{ SRP_OPT_MAX_CMD_PER_LUN,	"max_cmd_per_lun=%d" 	},
+	{ SRP_OPT_TARGET_CAN_QUEUE,	"target_can_queue=%d"	},
 	{ SRP_OPT_IO_CLASS,		"io_class=%x"		},
 	{ SRP_OPT_INITIATOR_EXT,	"initiator_ext=%s"	},
 	{ SRP_OPT_CMD_SG_ENTRIES,	"cmd_sg_entries=%u"	},
@@ -3724,6 +3737,15 @@ static int srp_parse_options(struct net *net, const char *buf,
 			target->scsi_host->cmd_per_lun = token;
 			break;
 
+		case SRP_OPT_TARGET_CAN_QUEUE:
+			if (match_int(args, &token) || token < 1) {
+				pr_warn("bad max target_can_queue parameter '%s'\n",
+					p);
+				goto out;
+			}
+			target->target_can_queue = token;
+			break;
+
 		case SRP_OPT_IO_CLASS:
 			if (match_hex(args, &token)) {
 				pr_warn("bad IO class parameter '%s'\n", p);
diff --git a/drivers/infiniband/ulp/srp/ib_srp.h b/drivers/infiniband/ulp/srp/ib_srp.h
index d66c9057d5ea..70334fa3de8e 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.h
+++ b/drivers/infiniband/ulp/srp/ib_srp.h
@@ -216,6 +216,7 @@ struct srp_target_port {
 	char			target_name[32];
 	unsigned int		scsi_id;
 	unsigned int		sg_tablesize;
+	unsigned int		target_can_queue;
 	int			mr_pool_size;
 	int			mr_per_cmd;
 	int			queue_size;

Bart.