Re: /sys/block/md126 still exists even after stopping the array

[NeilBrown <neilb@suse.de>]

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On Fri, 26 Sep 2014 14:50:08 +0200 Francis Moreau <francis.moro@gmail.com>
wrote:

> On 09/26/2014 02:21 PM, Francis Moreau wrote:
> [...]
> 
> > 
> >>>> mdadm --stop --scan <<<
> > 
> > [   89.975162] md_open(): md125 opened by mdadm [930]
> > [   89.975305] md_release(): md125 released by mdadm [930]
> > [   89.977434] md_open(): md125 opened by mdadm [932]
> > [   89.978813] md_open(): md125 opened by mdadm [930]
> > [   89.979365] md_release(): md125 released by mdadm [932]
> > [   89.979693] md_open(): md125 opened by systemd-udevd [931]
> > [   89.985790] md_release(): md125 released by systemd-udevd [931]
> > [   90.179911] md_release(): md125 released by mdadm [930]
> > [   90.180168] md_open(): md127 opened by mdadm [459]
> > [   90.180187] md_release(): md127 released by mdadm [459]
> > [   90.180199] md_open(): md126 opened by mdadm [459]
> > [   90.180205] md_release(): md126 released by mdadm [459]
> > [   90.180556] md_open(): md126 opened by mdadm [930]
> > [   90.180653] md_release(): md126 released by mdadm [930]
> > [   90.180690] md_open(): md126 opened by mdadm [930]
> > [   90.180758] md_open(): mdX opened by mdadm [459]
> 
> What is this 'mdX' device that mdadm operates on ?
> 
> It also doesn't have a counterpart release() call.

'mdX' is the name used if mddev->gendisk is NULL.
In that case, md_open() will return an error (ERESTARTSYS).
As the 'open' failed, we wouldn't expect a matching close/release.

NeilBrown


> 
> 
> > [   90.180995] md_open(): md125 opened by mdadm [459]
> > [   90.181056] md_release(): md125 released by mdadm [459]
> > [   90.182717] md_open(): md127 opened by mdadm [459]
> > [   90.182725] md_release(): md127 released by mdadm [459]
> > [   90.182732] md_open(): md126 opened by mdadm [459]
> > [   90.182761] md_release(): md126 released by mdadm [459]
> > [   90.182770] md_open(): md125 opened by mdadm [459]
> > [   90.182775] md_release(): md125 released by mdadm [459]
> > [   90.182940] md_release(): md126 released by mdadm [930]
> > [   90.183167] md_open(): md127 opened by mdadm [930]
> > [   90.183257] md_release(): md127 released by mdadm [930]
> > [   90.183288] md_open(): md127 opened by mdadm [930]
> > [   90.183461] md_open(): md127 opened by mdadm [459]
> > [   90.183488] md_release(): md127 released by mdadm [459]
> > [   90.183499] md_open(): md125 opened by mdadm [459]
> > [   90.183505] md_release(): md125 released by mdadm [459]
> > [   90.183686] md_release(): md127 released by mdadm [930]
> > 
> > 
> >> Probably there is a 'change' event happening just before the 'remove' event,
> >> and udev runs "mdadm" on the 'change' event, and that ends up happening after
> >> the device has been removed.
> >>
> >> Is this really a problem?  Can't you just ignore it and pretend it isn't
> >> there?
> > 
> > Well, if you list the block devices that the kernel detected in order to
> > operate on them, it could. I don't know exactly what would be the result
> > to use it but it could confuse some tools.
> > 
> > Is there a way to check that the 'ghost' device has been removed by
> > poking sysfs ?
> > 
> > Thanks
> > 
> 
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