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Commit 79b9677d authored by Kay Sievers's avatar Kay Sievers Committed by James Bottomley
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[SCSI] sr: check_events() ignore GET_EVENT when TUR says otherwise 



Some broken devices indicates that media has changed on every
GET_EVENT_STATUS_NOTIFICATION.  This translates into MEDIA_CHANGE
uevent on every open() which lets udev run into a loop.

Verify GET_EVENT result against TUR and if it generates spurious
events for several times in a row, 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

-tj: Updated to consider only spurious GET_EVENT events among
     different types of disagreement and allow using TUR for kernel
     event polling after GET_EVENT is ignored.

Reported-By: default avatarMarkus Rathgeb <maggu2810@googlemail.com>
Signed-off-by: default avatarKay Sievers <kay.sievers@vrfy.org>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: stable@kernel.org	# >= v2.6.38, fixes udev busy looping w/ certain devices
Signed-off-by: default avatarJames Bottomley <JBottomley@Parallels.com>
parent 57a6fa9a

drivers/scsi/sr.c

+42 −4
Original line number Diff line number Diff line
@@ -221,14 +221,33 @@ static unsigned int sr_check_events(struct cdrom_device_info *cdi, 
		return 0;



	events = sr_get_events(cd->device);

	cd->get_event_changed |= events & DISK_EVENT_MEDIA_CHANGE;



	/*

	 * If earlier GET_EVENT_STATUS_NOTIFICATION and TUR did not agree

	 * for several 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;

		goto do_tur;

	}



	/*

	 * GET_EVENT_STATUS_NOTIFICATION is enough unless MEDIA_CHANGE

	 * is being cleared.  Note that there are devices which hang

	 * if asked to execute TUR repeatedly.

	 */

	if (!(clearing & DISK_EVENT_MEDIA_CHANGE))

		goto skip_tur;

	if (cd->device->changed) {

		events |= DISK_EVENT_MEDIA_CHANGE;

		cd->device->changed = 0;

		cd->tur_changed = true;

	}



	if (!(clearing & DISK_EVENT_MEDIA_CHANGE))

		return events;

do_tur:

	/* 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);
@@ -242,12 +261,31 @@ static unsigned int sr_check_events(struct cdrom_device_info *cdi, 
		(scsi_sense_valid(&sshdr) && sshdr.asc != 0x3a);



	if (last_present != cd->media_present)

		events |= DISK_EVENT_MEDIA_CHANGE;

skip_tur:

		cd->device->changed = 1;



	if (cd->device->changed) {

		events |= DISK_EVENT_MEDIA_CHANGE;

		cd->device->changed = 0;

		cd->tur_changed = true;

	}



	if (cd->ignore_get_event)

		return events;



	/* check whether GET_EVENT is reporting spurious MEDIA_CHANGE */

	if (!cd->tur_changed) {

		if (cd->get_event_changed) {

			if (cd->tur_mismatch++ > 8) {

				sdev_printk(KERN_WARNING, cd->device,

					    "GET_EVENT and TUR disagree continuously, suppress GET_EVENT events\n");

				cd->ignore_get_event = true;

			}

		} else {

			cd->tur_mismatch = 0;

		}

	}

	cd->tur_changed = false;

	cd->get_event_changed = false;



	return events;

}

drivers/scsi/sr.h

+7 −0
Original line number Diff line number Diff line
@@ -41,6 +41,13 @@ 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 */



	/* GET_EVENT spurious event handling, blk layer guarantees exclusion */

	int tur_mismatch;		/* nr of get_event TUR mismatches */

	bool tur_changed:1;		/* changed according to TUR */

	bool get_event_changed:1;	/* changed according to GET_EVENT */

	bool ignore_get_event:1;	/* GET_EVENT is unreliable, use TUR */



	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 */