[systemd-devel] [PATCH] md: Drop sending a change uevent when stopping

[NeilBrown]

On Thu, Feb 18 2016, Shaohua Li wrote:

> On Wed, Feb 17, 2016 at 05:25:00PM +0100, Sebastian Parschauer wrote:
>> When stopping an MD device, then its device node /dev/mdX may still
>> exist afterwards or it is recreated by udev. The next open() call
>> can lead to creation of an inoperable MD device. The reason for
>> this is that a change event (KOBJ_CHANGE) is sent to udev which
>> races against the remove event (KOBJ_REMOVE) from md_free().
>> So drop sending the change event.
>> 
>> A change is likely also required in mdadm as many versions send the
>> change event to udev as well.
>
> Makes sense, it's unlikely we need the CHANGE event. Applied.
>
> Thanks,
> Shaohua

It would be worth checking, but I think that with this change, you can
write
  "inactive" to /sys/block/mdXXX/md/array_state
and the array will become inactive, but no uevent will be generated,
which isn't good.
Maybe send the uevent that was just removed from the 'inactive' case of
array_state_store() instead.

(But I still think this is just a bandaid and doesn't provide any
guarantees that there will be no races with udev)

NeilBrown
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