Re: udev queue error

[Kay Sievers <kay.sievers@vrfy.org>]

On Wed, 2011-06-15 at 11:40 +0200, Tejun Heo wrote:
> Hello,
> 
> On Wed, Jun 15, 2011 at 11:34:23AM +0200, Kay Sievers wrote:
> > Any idea why with the first check GET_EVENT seems, but TUR seems to
> > indicate no change?
> 
> That's probably because probing logic already consumed UA.  Reset
> during probe also causes UA so detection logic consumes them
> afterwards.  I don't think driver can tell apart different UAs at that
> point.  If the device determines to report media change after reset
> via GET_EVENT, you get a mismatch.  So, it's more or less expected.

Here is a new patch. Would be great, if one of you guys can check if it
fixes the loop we are currently seeing.

Thanks,
Kay

From: Kay Sievers <kay.sievers@vrfy.org>
Subject: sr: check_events() ignore GET_EVENT when TUR says otherwise

Some (broken) devices return GET_EVENT at every open() which
lets udev run into a loop when the device is accessed fron an
event handler.

When GET_EVENT and TUR disagree for a few times in a row,
we ignore the GET_EVENT events, and trust only the TUR status.

This is the log of a USB stick with a (broken) fake CDROM drive:
  scsi 5:0:0:0: Direct-Access     SanDisk  U3 Cruzer Micro  8.02 PQ: 0 ANSI: 0 CCS
  sd 5:0:0:0: Attached scsi generic sg3 type 0
  scsi 5:0:0:1: CD-ROM            SanDisk  U3 Cruzer Micro  8.02 PQ: 0 ANSI: 0
  sd 5:0:0:0: [sdb] Attached SCSI removable disk
  sr2: scsi3-mmc drive: 48x/48x tray
  sr 5:0:0:1: Attached scsi CD-ROM sr2
  sr 5:0:0:1: Attached scsi generic sg4 type 5
  sr2: GET_EVENT and TUR disagree continuously, suppress GET_EVENT events
  sd 5:0:0:0: [sdb] 31777279 512-byte logical blocks: (16.2 GB/15.1 GiB)
  sd 5:0:0:0: [sdb] No Caching mode page present
  sd 5:0:0:0: [sdb] Assuming drive cache: write through
  sd 5:0:0:0: [sdb] No Caching mode page present
  sd 5:0:0:0: [sdb] Assuming drive cache: write through
  sdb: sdb1

Reported-By: Markus Rathgeb maggu2810@googlemail.com
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
---

diff --git a/drivers/scsi/sr.c b/drivers/scsi/sr.c
index 4778e27..1b42dbd 100644
--- a/drivers/scsi/sr.c
+++ b/drivers/scsi/sr.c
@@ -229,6 +229,15 @@ static unsigned int sr_check_events(struct cdrom_device_info *cdi,
 	if (!(clearing & DISK_EVENT_MEDIA_CHANGE))
 		goto skip_tur;
 
+	/*
+	 * Earlier GET_EVENT_STATUS_NOTIFICATION and TUR did not agree
+	 * for a couple of times in a row. We rely on TUR only for this
+	 * likely broken device, to prevent generating incorrect media
+	 * changed events for every open().
+	 */
+	if (cd->ignore_get_event)
+		events &= ~DISK_EVENT_MEDIA_CHANGE;
+
 	/* let's see whether the media is there with TUR */
 	last_present = cd->media_present;
 	ret = scsi_test_unit_ready(cd->device, SR_TIMEOUT, MAX_RETRIES, &sshdr);
@@ -241,8 +250,19 @@ static unsigned int sr_check_events(struct cdrom_device_info *cdi,
 	cd->media_present = scsi_status_is_good(ret) ||
 		(scsi_sense_valid(&sshdr) && sshdr.asc != 0x3a);
 
-	if (last_present != cd->media_present)
+	if (last_present != cd->media_present) {
 		events |= DISK_EVENT_MEDIA_CHANGE;
+	} else if (events & DISK_EVENT_MEDIA_CHANGE) {
+		if (cd->tur_mismatch > 8) {
+			printk("%s: GET_EVENT and TUR disagree continuously, "
+			       "suppress GET_EVENT events\n", cd->cdi.name);
+			cd->ignore_get_event = true;
+		} else {
+			cd->tur_mismatch++;
+		}
+	} else if (!cd->ignore_get_event && cd->tur_mismatch > 0) {
+		cd->tur_mismatch = 0;
+	}
 skip_tur:
 	if (cd->device->changed) {
 		events |= DISK_EVENT_MEDIA_CHANGE;
diff --git a/drivers/scsi/sr.h b/drivers/scsi/sr.h
index e036f1d..94a3215 100644
--- a/drivers/scsi/sr.h
+++ b/drivers/scsi/sr.h
@@ -41,6 +41,8 @@ typedef struct scsi_cd {
 	unsigned readcd_known:1;	/* drive supports READ_CD (0xbe) */
 	unsigned readcd_cdda:1;	/* reading audio data using READ_CD */
 	unsigned media_present:1;	/* media is present */
+	unsigned ignore_get_event:1;	/* get_event is unreliable, use TUR */
+	int tur_mismatch;		/* nr of get_event TUR mismatches */
 	struct cdrom_device_info cdi;
 	/* We hold gendisk and scsi_device references on probe and use
 	 * the refs on this kref to decide when to release them */