[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: Markus Rathgeb maggu2810@googlemail.com
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@kernel.org	# >= v2.6.38, fixes udev busy looping w/ certain devices
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

diff --git a/drivers/scsi/sr.c b/drivers/scsi/sr.c
index 4778e27..5fc97d2 100644 (file)
--- a/drivers/scsi/sr.c
+++ b/drivers/scsi/sr.c
@@ -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;
 }

diff --git a/drivers/scsi/sr.h b/drivers/scsi/sr.h
index e036f1d..37c8f6b 100644 (file)
--- a/drivers/scsi/sr.h
+++ b/drivers/scsi/sr.h
@@ -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 */