[PATCH v4 2/5] scsi: core: Support setting BLK_MQ_F_BLOCKING

[Bart Van Assche <bvanassche@acm.org>]

Prepare for adding code in ufshcd_queuecommand() that may sleep. This
patch is similar to a patch posted last year by Mike Christie. See also
https://lore.kernel.org/all/20220308003957.123312-2-michael.christie@oracle.com/

Cc: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/scsi/hosts.c     |  1 +
 drivers/scsi/scsi_lib.c  | 11 ++++-------
 include/scsi/scsi_host.h |  6 ++++++
 3 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index f0bc8bbb3938..198edf03f929 100644
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c
@@ -441,6 +441,7 @@ struct Scsi_Host *scsi_host_alloc(const struct scsi_host_template *sht, int priv
 	shost->cmd_per_lun = sht->cmd_per_lun;
 	shost->no_write_same = sht->no_write_same;
 	shost->host_tagset = sht->host_tagset;
+	shost->queuecommand_may_block = sht->queuecommand_may_block;
 
 	if (shost_eh_deadline == -1 || !sht->eh_host_reset_handler)
 		shost->eh_deadline = -1;
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 5f29faa0560f..e0b5d35e7949 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1981,6 +1981,8 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
 	tag_set->flags = BLK_MQ_F_SHOULD_MERGE;
 	tag_set->flags |=
 		BLK_ALLOC_POLICY_TO_MQ_FLAG(shost->hostt->tag_alloc_policy);
+	if (shost->queuecommand_may_block)
+		tag_set->flags |= BLK_MQ_F_BLOCKING;
 	tag_set->driver_data = shost;
 	if (shost->host_tagset)
 		tag_set->flags |= BLK_MQ_F_TAG_HCTX_SHARED;
@@ -2969,13 +2971,8 @@ scsi_host_block(struct Scsi_Host *shost)
 		}
 	}
 
-	/*
-	 * SCSI never enables blk-mq's BLK_MQ_F_BLOCKING flag so
-	 * calling synchronize_rcu() once is enough.
-	 */
-	WARN_ON_ONCE(shost->tag_set.flags & BLK_MQ_F_BLOCKING);
-
-	synchronize_rcu();
+	/* Wait for ongoing scsi_queue_rq() calls to finish. */
+	blk_mq_wait_quiesce_done(&shost->tag_set);
 
 	return 0;
 }
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 0f29799efa02..70b7475dcf56 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -458,6 +458,9 @@ struct scsi_host_template {
 	/* True if the host uses host-wide tagspace */
 	unsigned host_tagset:1;
 
+	/* The queuecommand callback may block. See also BLK_MQ_F_BLOCKING. */
+	unsigned queuecommand_may_block:1;
+
 	/*
 	 * Countdown for host blocking with no commands outstanding.
 	 */
@@ -653,6 +656,9 @@ struct Scsi_Host {
 	/* True if the host uses host-wide tagspace */
 	unsigned host_tagset:1;
 
+	/* The queuecommand callback may block. See also BLK_MQ_F_BLOCKING. */
+	unsigned queuecommand_may_block:1;
+
 	/* Host responded with short (<36 bytes) INQUIRY result */
 	unsigned short_inquiry:1;