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Bug#638887: udev: cdrom_id process can not be killed

Jameson Graef Rollins wrote:

> If I keep everything else the same (same version of udev) I do *not*
> experience the problem with kernel:
> 2.6.38-2-amd64
> but I *do* experience the problem with kernels:
> 2.6.39-2-amd64
> 3.0.0-1-amd64
> If you really think it's worthwhile to try downgrading udev let me know,

Nah, that shouldn't be necessary.  Thanks for figuring out the kernel
regression range.

The only potentially problematic commit I could find is the following.
It might be worth testing with it backed out.

commit bf2253a6f00e
Author: Tejun Heo <tj@kernel.org>
Date:   Fri Apr 29 10:15:14 2011 +0200

    cdrom: always check_disk_change() on open
    cdrom_open() called check_disk_change() after the rest of open path
    succeeded which leads to the following bizarre behavior.
    * After media change, if the device opened without O_NONBLOCK,
      open_for_data() naturally fails with -ENOMEDIA and
      check_disk_change() is never called.  The media is known to be gone
      and the open failure makes it obvious to the userland but device
      invalidation never happens.
    * But if the device is opened with O_NONBLOCK, all the checks are
      bypassed and cdrom_open() doesn't notice that the media is not there
      and check_disk_change() is called and invalidation happens.
    There's nothing to be gained by avoiding calling check_disk_change()
    on open failure.  Common cases end up calling check_disk_change()
    anyway.  All we get is inconsistent behavior.
    Fix it by moving check_disk_change() invocation to the top of
    cdrom_open() so that it always gets called regardless of how the rest
    of open proceeds.
    Stable: 2.6.38
    Signed-off-by: Tejun Heo <tj@kernel.org>
    Reported-by: Amit Shah <amit.shah@redhat.com>
    Tested-by: Amit Shah <amit.shah@redhat.com>
    Cc: stable@kernel.org
    Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
index 514dd8efaf73..75fb965b8f72 100644
--- a/drivers/cdrom/cdrom.c
+++ b/drivers/cdrom/cdrom.c
@@ -986,6 +986,9 @@ int cdrom_open(struct cdrom_device_info *cdi, struct block_device *bdev, fmode_t
 	cdinfo(CD_OPEN, "entering cdrom_open\n"); 
+	/* open is event synchronization point, check events first */
+	check_disk_change(bdev);
 	/* if this was a O_NONBLOCK open and we should honor the flags,
 	 * do a quick open without drive/disc integrity checks. */
@@ -1012,9 +1015,6 @@ int cdrom_open(struct cdrom_device_info *cdi, struct block_device *bdev, fmode_t
 	cdinfo(CD_OPEN, "Use count for \"/dev/%s\" now %d\n",
 			cdi->name, cdi->use_count);
-	/* Do this on open.  Don't wait for mount, because they might
-	    not be mounting, but opening with O_NONBLOCK */
-	check_disk_change(bdev);
 	return 0;
 	if (CDROM_CAN(CDC_LOCK) && cdi->options & CDO_LOCK) {

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