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

[NeilBrown <neilb@suse.de>]

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On Fri, 26 Sep 2014 12:23:27 +0200 Francis Moreau <francis.moro@gmail.com>
wrote:

> Hello Neil,
> 
> On 09/26/2014 02:33 AM, NeilBrown wrote:
> > On Thu, 25 Sep 2014 18:12:07 +0200 Francis Moreau <francis.moro@gmail.com>
> > wrote:
> [...]
> >> I tried to find out what could have opened the md device by using fuser,
> >> but fuser reports no users.
> > 
> > It is probably a transient open/close.
> > 
> 
> If it's open/close wouldn't the 'close' part make the device disapear ?

No. It's ... complicated.

> 
> >>
> >> I took a look to the udev rules which are the one shipped by mdadm 3.3.2
> >> but nothing keep the device opened during the remove event.
> >>
> >> Could you give me some hints here to debug this ?
> > 
> > Modify md_open in drivers/md/md.c to add
> >    printk("Opened by %s\n", current->comm);
> > 
> > and build a new kernel.  That will tell you the name of the process which
> > opened the device.
> > 
> 
> I did that I also added a trace in md_release() but strangely no trace
> were outputed from there.

Without seeing your patch I can't guess what it happening, but I am *certain*
that md_release() would get called providing md_open didn't return an error.

It might be helpful to print out the pid and the md device number too
 task_tgid_vnr(current)
will give you the pid.
  mdname(mddev)
give the name of the device.

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?

NeilBrown

> 
> Here's the details of what I did:
> 
> --- %< ---
> [root@localhost ~]# cat /proc/mdstat
> Personalities : [raid1]
> md125 : active raid1 vdc1[1] vdb1[0]
>       65472 blocks super 1.0 [2/2] [UU]
> 
> md126 : active raid1 vdc2[1] vdb2[0]
>       209536 blocks super 1.2 [2/2] [UU]
> 
> md127 : active raid1 vdb3[0] vdc3[1]
>       1819584 blocks super 1.2 [2/2] [UU]
> 
> unused devices: <none>
> 
> [root@localhost ~]# mdadm --stop --scan
> 
> [root@localhost ~]# dmesg | grep md_
> [    1.474207] md_open(): opened by mdadm
> [    1.475316] md_open(): opened by mdadm
> [    1.492880] md_open(): opened by mdadm
> [    1.493201] md_open(): opened by mdadm
> [    1.494690] md_open(): opened by mdadm
> [    1.499369] md_open(): opened by mdadm
> [    1.533566] md_open(): opened by mdadm
> [    1.533697] md_open(): opened by mdadm
> [    1.554419] md_open(): opened by mdadm
> [    1.574451] md_open(): opened by mdadm
> [    1.574666] md_open(): opened by mdadm
> [    1.574877] md_open(): opened by mdadm
> [    1.576822] md_open(): opened by systemd-udevd
> [    1.576895] md_open(): opened by systemd-udevd
> [    1.577029] md_open(): opened by systemd-udevd
> [    1.581850] md_open(): opened by mdadm
> [    1.584054] md_open(): opened by systemd-udevd
> [    1.584770] md_open(): opened by mdadm
> [    1.585175] md_open(): opened by mdadm
> [    1.586328] md_open(): opened by systemd-udevd
> [    1.586933] md_open(): opened by systemd-udevd
> [    1.651265] md_open(): opened by mdadm
> [    1.651320] md_open(): opened by mdadm
> [    1.651364] md_open(): opened by mdadm
> [    1.651437] md_open(): opened by mdadm
> [    1.652376] md_open(): opened by mdadm
> [    1.652452] md_open(): opened by mdadm
> [   33.486704] md_open(): opened by mdadm
> [   33.489259] md_open(): opened by mdadm
> [   33.491000] md_open(): opened by mdadm
> [   33.491767] md_open(): opened by systemd-udevd
> [   33.692255] md_open(): opened by mdadm
> [   33.692288] md_open(): opened by mdadm
> [   33.692606] md_open(): opened by mdadm
> [   33.692858] md_open(): opened by mdadm
> [   33.692942] md_open(): opened by mdadm
> [   33.693237] md_open(): opened by mdadm
> [   33.694254] md_open(): opened by mdadm
> [   33.694275] md_open(): opened by mdadm
> [   33.694373] md_open(): opened by mdadm
> [   33.695558] md_open(): opened by mdadm
> [   33.695679] md_open(): opened by mdadm
> [   33.695855] md_open(): opened by mdadm
> [   33.695894] md_open(): opened by mdadm
> 
> [root@localhost ~]# ls /dev/md125
> /dev/md125
> 
> [root@localhost ~]# fuser /dev/md125
> 
> [root@localhost ~]# ps aux | grep "mdadm\|systemd-udevd"
> root       366  0.0  0.1  38172  1696 ?        Ss   06:04   0:00
> /usr/lib/systemd/systemd-udevd
> root       465  0.0  0.0   4964   924 ?        Ss   06:04   0:00
> /sbin/mdadm --monitor --scan --daemonise --syslog
> --pid-file=/run/mdadm/mdadm.pid
> 
> [root@localhost ~]# ls -l /proc/366/fd/
> total 0
> lrwx------ 1 root root 64 Sep 26 06:04 0 -> /dev/null
> lrwx------ 1 root root 64 Sep 26 06:04 1 -> /dev/null
> lrwx------ 1 root root 64 Sep 26 06:04 10 -> socket:[8665]
> lr-x------ 1 root root 64 Sep 26 06:04 11 -> /etc/udev/hwdb.bin
> lrwx------ 1 root root 64 Sep 26 06:04 12 -> anon_inode:[eventpoll]
> lrwx------ 1 root root 64 Sep 26 06:04 2 -> /dev/null
> lrwx------ 1 root root 64 Sep 26 06:04 3 -> socket:[8144]
> lrwx------ 1 root root 64 Sep 26 06:04 4 -> socket:[8103]
> lrwx------ 1 root root 64 Sep 26 06:04 5 -> socket:[8660]
> lrwx------ 1 root root 64 Sep 26 06:04 6 -> /run/udev/queue.bin
> lr-x------ 1 root root 64 Sep 26 06:04 7 -> anon_inode:inotify
> lrwx------ 1 root root 64 Sep 26 06:04 8 -> anon_inode:[signalfd]
> lrwx------ 1 root root 64 Sep 26 06:04 9 -> socket:[8664]
> 
> [root@localhost ~]# ls -l /proc/465/fd/
> total 0
> lrwx------ 1 root root 64 Sep 26 06:04 0 -> /dev/null
> lrwx------ 1 root root 64 Sep 26 06:04 1 -> /dev/null
> lrwx------ 1 root root 64 Sep 26 06:04 2 -> /dev/null
> lr-x------ 1 root root 64 Sep 26 06:06 4 -> /proc/mdstat
> lrwx------ 1 root root 64 Sep 26 06:06 5 -> socket:[10038]
> 
> [root@localhost ~]# cat /proc/mdstat
> Personalities : [raid1]
> unused devices: <none>
> 
> [root@localhost ~]# ls /sys/block/md125/md/
> array_size  array_state  bitmap/  chunk_size  component_size  layout
> level  max_read_errors  metadata_version  new_dev  raid_disks
> reshape_direction  reshape_position  resync_start  safe_mode_delay
> 
> --- >% ---
> 
> So in my understanding, only mdadm and udevd are opening the MD devices
> and mdamd was the last to open the device. For some unknown reasons,
> md_release() is never called.
> 
> This happens with:
> 
>  - kernel 3.14.19
>  - mdadm 3.3.2
>  - systemd 208
> 
> Can you see something wrong here ?
> 
> Thanks.
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