On Wed, Aug 30 2017, Xiao Ni wrote: > Hi Neil > > I have searched in history emails and there have many topics like this. Sorry for talking > about this again. But it looks like the situation I encountered is different. There is 1 second > window between stop the raid device and delete the node /dev/md0. The /dev/md0 node can be > removed successfully after 1 second. I think you are saying that /dev/md0 gets deleted 1 second after the device is stopped. I assume that is a delay in udev processing of events. When you say "can be" I assume you mean "is being". ie. if you say "The node can be removed after 1 second", it seems to imply that if you try to remove it earlier, the unlink() will fail. If you say "The node is being removed after 1 seconds", that suggests that the removal happens automatically, but there is a delay between the device stopping and the removal happening. > > There is no process that open the /dev/md0 after mdadm -S /dev/md0: > > mdadm -CR /dev/md0 -l1 -n2 /dev/loop0 /dev/loop1 --assume-clean > dmesg: > [36416.860525] Opened by mdadm, pid is 3523 > [36416.984160] md/raid1:md0: active with 2 out of 2 mirrors > [36416.984181] md0: detected capacity change from 0 to 523239424 > [36416.984219] Released by mdadm, pid is 3523 > [36416.984228] remove_and_add_spares > [36416.991588] Opened by mdadm, pid is 3541 > [36416.997183] Released by mdadm, pid is 3541 > [36417.001376] Opened by systemd-udevd, pid is 3525 > [36417.007128] Released by systemd-udevd, pid is 3525 > > udev: > KERNEL[36419.830817] add /devices/virtual/bdi/9:0 (bdi) > KERNEL[36419.831045] add /devices/virtual/block/md0 (block) > UDEV [36419.832911] add /devices/virtual/bdi/9:0 (bdi) > UDEV [36419.836380] add /devices/virtual/block/md0 (block) > KERNEL[36419.877705] change /devices/virtual/block/loop0 (block) > KERNEL[36419.878057] change /devices/virtual/block/loop0 (block) > KERNEL[36419.926761] change /devices/virtual/block/loop1 (block) > KERNEL[36419.927015] change /devices/virtual/block/loop1 (block) > UDEV [36419.953112] change /devices/virtual/block/loop0 (block) > UDEV [36419.953141] change /devices/virtual/block/loop1 (block) > KERNEL[36419.954765] change /devices/virtual/block/md0 (block) > UDEV [36419.955973] change /devices/virtual/block/loop0 (block) > UDEV [36419.962799] change /devices/virtual/block/loop1 (block) > UDEV [36419.982934] change /devices/virtual/block/md0 (block) > > mdadm -S /dev/md0 > dmesg: > [36493.068054] Opened by mdadm, pid is 3552 > [36493.072051] Released by mdadm, pid is 3552 > [36493.076123] Opened by mdadm, pid is 3552 > [36493.080073] md0: detected capacity change from 523239424 to 0 > [36493.080077] md: md0 stopped. > [36493.273011] Released by mdadm, pid is 3552 > udev: > KERNEL[36496.300219] remove /devices/virtual/bdi/9:0 (bdi) > KERNEL[36496.300335] remove /devices/virtual/block/md0 (block) > UDEV [36496.300736] remove /devices/virtual/bdi/9:0 (bdi) > UDEV [36496.301812] remove /devices/virtual/block/md0 (block) I don't see any 1 second delay here. I can see a 3 second delay between "Released by mdadm, pid = 3552" and the UDEV remove event. Is that what you are referring to? > > There are only REMOVE events during command mdadm -S /dev/md0. The remove events seems to happen *after* "mdadm -S /dev/md0", or did "mdadm -S /dev/md0" take 3 seconds to run? > > I tried to create a lvm and remove it to check whether lvm has this problem or not. > > pvcreate /dev/md0 > vgcreate vg /dev/md0 > lvcreate -L 100M -n test vg > lvremove vg/test -y > ls /dev/mapper/vg-test > ls /dev/dm-3 > > The node /dev/mapper/vg-test and /dev/dm-3 can be removed in time. There is no time > window. So it looks like it's a problem of md. Could you give some suggestions about > this? What should I do next? Maybe lvremove explicitly unlinks the files in /dev, I don't know. > > If it's not a bug, why there is a 1 second window? As I said, probably because udev is slow. Why do you think this is a problem? Why do you care about 1 second window. If I don't know how why this matters, I cannot help you. NeilBrown
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