On 09/26/2014 12:44 PM, NeilBrown wrote:

quoted

On Fri, 26 Sep 2014 12:23:27 +0200 Francis Moreau [off-list ref]
wrote:

quoted

Hello Neil,

On 09/26/2014 02:33 AM, NeilBrown wrote:

quoted

On Thu, 25 Sep 2014 18:12:07 +0200 Francis Moreau [off-list ref]
wrote:

[...]

quoted

quoted

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.

quoted

quoted

quoted

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.

Here's the patch:

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 73aedcb..08ead8d 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c

@@ -6703,6 +6703,8 @@ static int md_open(struct block_device *bdev,

fmode_t mode)
 	struct mddev *mddev = mddev_find(bdev->bd_dev);
 	int err;

+	printk("md_open(): opened by %s\n", current->comm);
+
 	if (!mddev)
 		return -ENODEV;

@@ -6735,6 +6737,8 @@ static void md_release(struct gendisk *disk,

fmode_t mode)
 {
  	struct mddev *mddev = disk->private_data;

+	printk("md_release(): released by %s\n", current->comm);
+
 	BUG_ON(!mddev);
 	atomic_dec(&mddev->openers);
 	mddev_put(mddev);

quoted

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.

Here's the new trace, this time md_release() was called, so I probably
did something wrong the first time, sorry for that.

[    1.470744] md_open(): md127 opened by mdadm [388]
[    1.485437] md_release(): md127 released by mdadm [388]
[    1.486888] md_open(): md126 opened by mdadm [381]
[    1.487468] md_release(): md126 released by mdadm [381]
[    1.488646] md_open(): md125 opened by mdadm [383]
[    1.489074] md_release(): md125 released by mdadm [383]
[    1.490555] md_open(): md127 opened by mdadm [385]
[    1.512556] md_release(): md127 released by mdadm [385]
[    1.512582] md_open(): md127 opened by mdadm [385]
[    1.512682] md_open(): md126 opened by mdadm [384]
[    1.553414] md_release(): md126 released by mdadm [384]
[    1.553442] md_open(): md126 opened by mdadm [384]
[    1.553549] md_open(): md125 opened by mdadm [382]
[    1.573263] md_release(): md125 released by mdadm [382]
[    1.573288] md_open(): md125 opened by mdadm [382]
[    1.601034] md_open(): md125 opened by mdadm [459]
[    1.601041] md_release(): md125 released by mdadm [459]
[    1.601065] md_open(): md126 opened by mdadm [459]
[    1.601067] md_release(): md126 released by mdadm [459]
[    1.601090] md_open(): md127 opened by mdadm [459]
[    1.601092] md_release(): md127 released by mdadm [459]
[    1.601130] md_open(): md127 opened by mdadm [459]
[    1.601220] md_release(): md127 released by mdadm [459]
[    1.601633] md_open(): md126 opened by mdadm [459]
[    1.601661] md_release(): md126 released by mdadm [459]
[    1.601673] md_open(): md125 opened by mdadm [459]
[    1.601695] md_release(): md125 released by mdadm [459]
[    1.606127] md_open(): md125 opened by mdadm [454]
[    1.608682] md_open(): md126 opened by mdadm [453]
[    1.609514] md_open(): md127 opened by mdadm [448]
[    1.622512] md_release(): md126 released by mdadm [453]
[    1.623028] md_release(): md127 released by mdadm [448]
[    1.625288] md_open(): md126 opened by systemd-udevd [363]
[    1.625391] md_release(): md125 released by mdadm [454]
[    1.625619] md_open(): md127 opened by systemd-udevd [368]
[    1.625737] md_open(): md125 opened by systemd-udevd [366]
[    1.637137] md_release(): md125 released by systemd-udevd [366]
[    1.643982] md_open(): md125 opened by mdadm [476]
[    1.644071] md_release(): md127 released by systemd-udevd [368]
[    1.647787] md_release(): md125 released by mdadm [382]
[    1.648171] md_release(): md126 released by systemd-udevd [363]
[    1.651629] md_open(): md126 opened by mdadm [479]
[    1.656666] md_open(): md127 opened by mdadm [480]
[    1.657771] md_release(): md125 released by mdadm [476]
[    1.659312] md_open(): md125 opened by systemd-udevd [365]
[    1.663193] md_release(): md127 released by mdadm [385]
[    1.673669] md_release(): md125 released by systemd-udevd [365]
[    1.685527] md_release(): md127 released by mdadm [480]
[    1.685599] md_release(): md126 released by mdadm [479]
[    1.686058] md_open(): md126 opened by systemd-udevd [366]
[    1.686282] md_release(): md126 released by systemd-udevd [366]
[    1.691024] md_open(): md127 opened by systemd-udevd [363]
[    1.695415] md_release(): md126 released by mdadm [384]
[    1.707163] md_release(): md127 released by systemd-udevd [363]

quoted

quoted

quoted

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]
[   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]