scsi: srp_transport: Move queuecommand() wait code to SCSI core

Additionally, rename srp_wait_for_queuecommand() into
scsi_wait_for_queuecommand() and add a comment about the queuecommand()
call from scsi_send_eh_cmnd().

Note: this patch changes scsi_internal_device_block from a function that
did not sleep into a function that may sleep. This is fine for all
callers of this function:

* scsi_internal_device_block() is called from the mpt3sas device while
  that driver holds the ioc->dm_cmds.mutex. This means that the mpt3sas
  driver calls this function from thread context.
* scsi_target_block() is called by __iscsi_block_session() from
  kernel thread context and with IRQs enabled.
* The SRP transport code also calls scsi_target_block() from kernel
  thread context while sleeping is allowed.
* The snic driver also calls scsi_target_block() from a context from
  which sleeping is allowed. The scsi_target_block() call namely occurs
  immediately after a scsi_flush_work() call.

[mkp: s/shost/sdev/]

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Cc: James Bottomley <jejb@linux.vnet.ibm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Doug Ledford <dledford@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_lib.c

@@ -2733,6 +2733,39 @@ void sdev_evt_send_simple(struct scsi_device *sdev,
 }
 EXPORT_SYMBOL_GPL(sdev_evt_send_simple);
 
+/**
+ * scsi_request_fn_active() - number of kernel threads inside scsi_request_fn()
+ * @sdev: SCSI device to count the number of scsi_request_fn() callers for.
+ */
+static int scsi_request_fn_active(struct scsi_device *sdev)
+{
+	struct request_queue *q = sdev->request_queue;
+	int request_fn_active;
+
+	WARN_ON_ONCE(sdev->host->use_blk_mq);
+
+	spin_lock_irq(q->queue_lock);
+	request_fn_active = q->request_fn_active;
+	spin_unlock_irq(q->queue_lock);
+
+	return request_fn_active;
+}
+
+/**
+ * scsi_wait_for_queuecommand() - wait for ongoing queuecommand() calls
+ * @sdev: SCSI device pointer.
+ *
+ * Wait until the ongoing shost->hostt->queuecommand() calls that are
+ * invoked from scsi_request_fn() have finished.
+ */
+static void scsi_wait_for_queuecommand(struct scsi_device *sdev)
+{
+	WARN_ON_ONCE(sdev->host->use_blk_mq);
+
+	while (scsi_request_fn_active(sdev))
+		msleep(20);
+}
+
 /**
  *	scsi_device_quiesce - Block user issued commands.
  *	@sdev:	scsi device to quiesce.
@@ -2817,8 +2850,7 @@ EXPORT_SYMBOL(scsi_target_resume);
  * @sdev:	device to block
  *
  * Block request made by scsi lld's to temporarily stop all
- * scsi commands on the specified device.  Called from interrupt
+ * scsi commands on the specified device. May sleep.
- * or normal process context.
  *
  * Returns zero if successful or error if not
  *
@@ -2827,6 +2859,10 @@ EXPORT_SYMBOL(scsi_target_resume);
  *	(which must be a legal transition).  When the device is in this
  *	state, all commands are deferred until the scsi lld reenables
  *	the device with scsi_device_unblock or device_block_tmo fires.
+ *
+ * To do: avoid that scsi_send_eh_cmnd() calls queuecommand() after
+ * scsi_internal_device_block() has blocked a SCSI device and also
+ * remove the rport mutex lock and unlock calls from srp_queuecommand().
  */
 int
 scsi_internal_device_block(struct scsi_device *sdev)
@@ -2854,6 +2890,7 @@ scsi_internal_device_block(struct scsi_device *sdev)
 		spin_lock_irqsave(q->queue_lock, flags);
 		blk_stop_queue(q);
 		spin_unlock_irqrestore(q->queue_lock, flags);
+		scsi_wait_for_queuecommand(sdev);
 	}
 
 	return 0;

drivers/scsi/scsi_transport_srp.c

@@ -24,7 +24,6 @@
 #include <linux/err.h>
 #include <linux/slab.h>
 #include <linux/string.h>
-#include <linux/delay.h>
 
 #include <scsi/scsi.h>
 #include <scsi/scsi_cmnd.h>
@@ -393,36 +392,6 @@ static void srp_reconnect_work(struct work_struct *work)
 	}
 }
 
-/**
- * scsi_request_fn_active() - number of kernel threads inside scsi_request_fn()
- * @shost: SCSI host for which to count the number of scsi_request_fn() callers.
- *
- * To do: add support for scsi-mq in this function.
- */
-static int scsi_request_fn_active(struct Scsi_Host *shost)
-{
-	struct scsi_device *sdev;
-	struct request_queue *q;
-	int request_fn_active = 0;
-
-	shost_for_each_device(sdev, shost) {
-		q = sdev->request_queue;
-
-		spin_lock_irq(q->queue_lock);
-		request_fn_active += q->request_fn_active;
-		spin_unlock_irq(q->queue_lock);
-	}
-
-	return request_fn_active;
-}
-
-/* Wait until ongoing shost->hostt->queuecommand() calls have finished. */
-static void srp_wait_for_queuecommand(struct Scsi_Host *shost)
-{
-	while (scsi_request_fn_active(shost))
-		msleep(20);
-}
-
 static void __rport_fail_io_fast(struct srp_rport *rport)
 {
 	struct Scsi_Host *shost = rport_to_shost(rport);
@@ -432,14 +401,17 @@ static void __rport_fail_io_fast(struct srp_rport *rport)
 
 	if (srp_rport_set_state(rport, SRP_RPORT_FAIL_FAST))
 		return;
+	/*
+	 * Call scsi_target_block() to wait for ongoing shost->queuecommand()
+	 * calls before invoking i->f->terminate_rport_io().
+	 */
+	scsi_target_block(rport->dev.parent);
 	scsi_target_unblock(rport->dev.parent, SDEV_TRANSPORT_OFFLINE);
 
 	/* Involve the LLD if possible to terminate all I/O on the rport. */
 	i = to_srp_internal(shost->transportt);
-	if (i->f->terminate_rport_io) {
+	if (i->f->terminate_rport_io)
-		srp_wait_for_queuecommand(shost);
 		i->f->terminate_rport_io(rport);
-	}
 }
 
 /**
@@ -567,7 +539,6 @@ int srp_reconnect_rport(struct srp_rport *rport)
 	if (res)
 		goto out;
 	scsi_target_block(&shost->shost_gendev);
-	srp_wait_for_queuecommand(shost);
 	res = rport->state != SRP_RPORT_LOST ? i->f->reconnect(rport) : -ENODEV;
 	pr_debug("%s (state %d): transport.reconnect() returned %d\n",
 		 dev_name(&shost->shost_gendev), rport->state, res);