Re: [PATCH] scsi: avoid repetitive logging of device offline messages

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On 3/9/20 11:14 AM, Ewan D. Milne wrote:
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.

Signed-off-by: Ewan D. Milne <emilne@xxxxxxxxxx>
---
  drivers/scsi/scsi_lib.c    | 8 ++++++--
  include/scsi/scsi_device.h | 2 ++
  2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 610ee41..d3a6d97 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1240,8 +1240,11 @@ 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 = 1;
+			sdev_printk(KERN_ERR, sdev,
+				    "rejecting I/O to offline device\n");
+		}
  		return BLK_STS_IOERR;
  	case SDEV_DEL:
  		/*
@@ -2340,6 +2343,7 @@ scsi_device_set_state(struct scsi_device *sdev, enum scsi_device_state state)
  		break;
}
+	sdev->offline_already = 0;
  	sdev->sdev_state = state;
  	return 0;
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index f8312a3..72987a0 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -204,6 +204,8 @@ 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 */
+	unsigned offline_already:1;	/* Device offline message logged */
+
  	atomic_t disk_events_disable_depth; /* disable depth for disk events */
DECLARE_BITMAP(supported_events, SDEV_EVT_MAXBITS); /* supported events */

Bitfields are troublesome in multithreaded software. Has it been considered to use rate-limiting instead of introducing a new bitfield member?

Thanks,

Bart.





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