Patch "scsi: core: Ensure that the SCSI error handler gets woken up" has been added to the 4.14-stable tree

@@ -318,6 +318,9 @@ static void scsi_host_dev_release(struct
 
 	scsi_proc_hostdir_rm(shost->hostt);
 
+	/* Wait for functions invoked through call_rcu(&shost->rcu, ...) */
+	rcu_barrier();
+
 	if (shost->tmf_work_q)
 		destroy_workqueue(shost->tmf_work_q);
 	if (shost->ehandler)

@@ -325,6 +328,8 @@ static void scsi_host_dev_release(struct
 	if (shost->work_q)
 		destroy_workqueue(shost->work_q);
 
+	destroy_rcu_head(&shost->rcu);
+
 	if (shost->shost_state == SHOST_CREATED) {
 		/*
 		 * Free the shost_dev device name here if scsi_host_alloc()

@@ -399,6 +404,7 @@ struct Scsi_Host *scsi_host_alloc(struct
 	INIT_LIST_HEAD(&shost->starved_list);
 	init_waitqueue_head(&shost->host_wait);
 	mutex_init(&shost->scan_mutex);
+	init_rcu_head(&shost->rcu);
 
 	index = ida_simple_get(&host_index_ida, 0, 0, GFP_KERNEL);
 	if (index < 0)

@@ -220,6 +220,17 @@ static void scsi_eh_reset(struct scsi_cm
 	}
 }
 
+static void scsi_eh_inc_host_failed(struct rcu_head *head)
+{
+	struct Scsi_Host *shost = container_of(head, typeof(*shost), rcu);
+	unsigned long flags;
+
+	spin_lock_irqsave(shost->host_lock, flags);
+	shost->host_failed++;
+	scsi_eh_wakeup(shost);
+	spin_unlock_irqrestore(shost->host_lock, flags);
+}
+
 /**
  * scsi_eh_scmd_add - add scsi cmd to error handling.
  * @scmd:	scmd to run eh on.

@@ -242,9 +253,12 @@ void scsi_eh_scmd_add(struct scsi_cmnd *
 
 	scsi_eh_reset(scmd);
 	list_add_tail(&scmd->eh_entry, &shost->eh_cmd_q);
-	shost->host_failed++;
-	scsi_eh_wakeup(shost);
 	spin_unlock_irqrestore(shost->host_lock, flags);
+	/*
+	 * Ensure that all tasks observe the host state change before the
+	 * host_failed change.
+	 */
+	call_rcu(&shost->rcu, scsi_eh_inc_host_failed);
 }
 
 /**

@@ -318,22 +318,39 @@ static void scsi_init_cmd_errh(struct sc
 		cmd->cmd_len = scsi_command_size(cmd->cmnd);
 }
 
-void scsi_device_unbusy(struct scsi_device *sdev)
+/*
+ * Decrement the host_busy counter and wake up the error handler if necessary.
+ * Avoid as follows that the error handler is not woken up if shost->host_busy
+ * == shost->host_failed: use call_rcu() in scsi_eh_scmd_add() in combination
+ * with an RCU read lock in this function to ensure that this function in its
+ * entirety either finishes before scsi_eh_scmd_add() increases the
+ * host_failed counter or that it notices the shost state change made by
+ * scsi_eh_scmd_add().
+ */
+static void scsi_dec_host_busy(struct Scsi_Host *shost)
 {
-	struct Scsi_Host *shost = sdev->host;
-	struct scsi_target *starget = scsi_target(sdev);
 	unsigned long flags;
 
+	rcu_read_lock();
 	atomic_dec(&shost->host_busy);
-	if (starget->can_queue > 0)
-		atomic_dec(&starget->target_busy);
-
-	if (unlikely(scsi_host_in_recovery(shost) &&
-		     (shost->host_failed || shost->host_eh_scheduled))) {
+	if (unlikely(scsi_host_in_recovery(shost))) {
 		spin_lock_irqsave(shost->host_lock, flags);
-		scsi_eh_wakeup(shost);
+		if (shost->host_failed || shost->host_eh_scheduled)
+			scsi_eh_wakeup(shost);
 		spin_unlock_irqrestore(shost->host_lock, flags);
 	}
+	rcu_read_unlock();
+}
+
+void scsi_device_unbusy(struct scsi_device *sdev)
+{
+	struct Scsi_Host *shost = sdev->host;
+	struct scsi_target *starget = scsi_target(sdev);
+
+	scsi_dec_host_busy(shost);
+
+	if (starget->can_queue > 0)
+		atomic_dec(&starget->target_busy);
 
 	atomic_dec(&sdev->device_busy);
 }

@@ -1532,7 +1549,7 @@ starved:
 		list_add_tail(&sdev->starved_entry, &shost->starved_list);
 	spin_unlock_irq(shost->host_lock);
 out_dec:
-	atomic_dec(&shost->host_busy);
+	scsi_dec_host_busy(shost);
 	return 0;
 }
 

@@ -1993,7 +2010,7 @@ static blk_status_t scsi_queue_rq(struct
 	return BLK_STS_OK;
 
 out_dec_host_busy:
-	atomic_dec(&shost->host_busy);
+	scsi_dec_host_busy(shost);
 out_dec_target_busy:
 	if (scsi_target(sdev)->can_queue > 0)
 		atomic_dec(&scsi_target(sdev)->target_busy);

@@ -571,6 +571,8 @@ struct Scsi_Host {
 		struct blk_mq_tag_set	tag_set;
 	};
 
+	struct rcu_head rcu;
+
 	atomic_t host_busy;		   /* commands actually active on low-level */
 	atomic_t host_blocked;