[dm-devel] dmsetup remove gives EBUSY (even though it shouldn't be busy)

[Johannes Bauer]

Hey Milan,

sorry for the late answer -- I thought nobody replied to the topic
because I had the grouping setting messed up in my mail client. Only now
that I looked in the messages again because of something totally
unrelated I saw your response.

On 25.05.2015 14:38, Milan Broz wrote:

>> Afterwards I fork/exec the command "dmsetup remove foobar". This yields:
>>
>> device-mapper: remove ioctl on foobar failed: Device or resource busy
>> Command failed
> 
> Usually this is caused by running blkid (automatically running from udev rules)
> which react to close-on-write on the device and keep the device open while scanning.
> (You can try to run lsof, there is a chance you will see the process blocking
> this device.)

Ah, yes, indeed I do see a blkid process there.

> Recent device mapper tries to retry removal operation, so if you use
> recent dmsetup (or cryptsetup close command) you should see that it
> tries several times.

Yes, I saw that option, but in some cases it wouldn't wait long enough
in my case and still return EBUSY.

> First option is to disable WATCH rule in udev rules and check if this helps.
> (Unfortunately this has some side effects.)
> 
> Better solution is probably explicitly call "udevadm settle" instead
> of sleep(). Still not perfect (it waits for all devices/udev processes),
> but I am afraid there is nothing better yet to synchronize with these scans.

Hm, I don't think I want a change in the udev config, so I'm going to
navigate around this issue somhow. In any case my main worry was that I
was doing something wrong which would cause this behavior. That udev
calls blkid which causes the EBUSY actually is a good thing (because I
can reasonably assume that blkid will terminate after a rather short
amount of time).

So I thank you for your response, clearing this up.

Best regards,
Johannes