scsi: core: avoid repetitive logging of device offline messages

Large queues of I/O to offline devices that are eventually submitted when
devices are unblocked result in a many repeated "rejecting I/O to offline
device" messages.  These messages can fill up the dmesg buffer in crash
dumps so no useful prior messages remain.  In addition, if a serial console
is used, the flood of messages can cause a hard lockup in the console code.

Introduce a flag indicating the message has already been logged for the
device, and reset the flag when scsi_device_set_state() changes the device
state.

Link: https://lore.kernel.org/r/20200311143930.20674-1-emilne@redhat.comReviewed-by: Bart van Assche <bvanassche@acm.org>
Signed-off-by: Ewan D. Milne <emilne@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_lib.c

@@ -1215,8 +1215,11 @@ scsi_prep_state_check(struct scsi_device *sdev, struct request *req)
 		 * commands.  The device must be brought online
 		 * before trying any recovery commands.
 		 */
-		sdev_printk(KERN_ERR, sdev,
-			    "rejecting I/O to offline device\n");
+		if (!sdev->offline_already) {
+			sdev->offline_already = true;
+			sdev_printk(KERN_ERR, sdev,
+				    "rejecting I/O to offline device\n");
+		}
 		return BLK_STS_IOERR;
 	case SDEV_DEL:
 		/*
@@ -2326,6 +2329,7 @@ scsi_device_set_state(struct scsi_device *sdev, enum scsi_device_state state)
 		break;
 
 	}
+	sdev->offline_already = false;
 	sdev->sdev_state = state;
 	return 0;
 

include/scsi/scsi_device.h

@@ -203,6 +203,9 @@ struct scsi_device {
 	unsigned unmap_limit_for_ws:1;	/* Use the UNMAP limit for WRITE SAME */
 	unsigned rpm_autosuspend:1;	/* Enable runtime autosuspend at device
 					 * creation time */
+
+	bool offline_already;		/* Device offline message logged */
+
 	atomic_t disk_events_disable_depth; /* disable depth for disk events */
 
 	DECLARE_BITMAP(supported_events, SDEV_EVT_MAXBITS); /* supported events */