Hi Eric, On 2019/09/20 23:10, Eric Harney wrote:

On 9/20/19 1:52 AM, Rikimaru Honjo wrote:

...

Hi,

I'm using Queens cinder with the following setting.

--------------------------------- [coordination] backend_url = file://$state_path ---------------------------------

As a result, the files like the following were remained under the state path after some operations.[1]

cinder-63dacb3d-bd4d-42bb-88fe-6e4180164765-delete_volume cinder-32c426af-82b4-41de-b637-7d76fed69e83-delete_snapshot

In my understanding, these are lock-files created for synchronization by tooz. But, these lock-files were not deleted after finishing operations. Is this behaviour correct?

[1] e.g. Delete volume, Delete snapshot

This is a known bug that's described here:

https://github.com/harlowja/fasteners/issues/26

(The fasteners library is used by tooz, which is used by Cinder for managing these lock files.)

There's an old Cinder bug for it here: https://bugs.launchpad.net/cinder/+bug/1432387

but that's marked as "Won't Fix" because Cinder needs it to be fixed in the underlying libraries. Thank you for your explanation. I understood the state.

But, I have one more question. Can I think this bug doesn't affect synchronization? Best regards,

Thanks, Eric

-- _/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/ Rikimaru Honjo E-mail:honjo.rikimaru@ntt-tx.co.jp

On 2019/09/28 1:44, Ben Nemec wrote:

On 9/23/19 11:42 PM, Rikimaru Honjo wrote:

...

Hi Eric,

On 2019/09/20 23:10, Eric Harney wrote:

...

On 9/20/19 1:52 AM, Rikimaru Honjo wrote:

...

Hi,

I'm using Queens cinder with the following setting.

--------------------------------- [coordination] backend_url = file://$state_path ---------------------------------

As a result, the files like the following were remained under the state path after some operations.[1]

cinder-63dacb3d-bd4d-42bb-88fe-6e4180164765-delete_volume cinder-32c426af-82b4-41de-b637-7d76fed69e83-delete_snapshot

In my understanding, these are lock-files created for synchronization by tooz. But, these lock-files were not deleted after finishing operations. Is this behaviour correct?

[1] e.g. Delete volume, Delete snapshot

This is a known bug that's described here:

https://github.com/harlowja/fasteners/issues/26

(The fasteners library is used by tooz, which is used by Cinder for managing these lock files.)

There's an old Cinder bug for it here: https://bugs.launchpad.net/cinder/+bug/1432387

but that's marked as "Won't Fix" because Cinder needs it to be fixed in the underlying libraries. Thank you for your explanation. I understood the state.

But, I have one more question. Can I think this bug doesn't affect synchronization?

It does not. In fact, it's important to not remove lock files while a service is running or you can end up with synchronization issues.

To clean up the leftover lock files, we generally recommend clearing the lock_path for each service on reboot before the services have started.

Thank you for your information. I think that I understood this issue completely. Best Regards,

...

Best regards,

...

Thanks, Eric

-- _/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/ Rikimaru Honjo E-mail:honjo.rikimaru@ntt-tx.co.jp

On 10/15/19 7:48 AM, Herve Beraud wrote:

I proposed some patches through heat templates and puppet-cinder to remove lock files older than 1 week and avoid file system growing.

This is a solution based on a cron job, to fix that on stable branches, in a second time I'll help the fasteners project to fix the root cause by reviewing and testing the proposed patch (lock based on file offset). In next versions I hope we will use a patched fasteners and so we could drop the cron based solution.

Please can you give /reviews/feedbacks: - https://review.opendev.org/688413 - https://review.opendev.org/688414 - https://review.opendev.org/688415

I'm rather hesitant to recommend this. It looks like the change is only removing the -delete lock files, which are a fraction of the total lock files created by Cinder, and I don't particularly want to encourage people to start monkeying with the lock files while a service is running. Even with this limited set of deletions, I think we need a Cinder person to look and verify that we aren't making bad assumptions about how the locks are used. In essence, I don't think this is going to meaningfully reduce the amount of leftover lock files and it sets a bad precedent for how to handle them. Personally, I'd rather see a boot-time service added for each OpenStack service that goes out and wipes the lock file directory before starting the service. On a more general note, I'm going to challenge the assertion that "Customer file system growing slowly and so customer risk to facing some issues to file system usage after a long period." I have yet to hear an actual bug report from the leftover lock files. Every time this comes up it's because someone noticed a lot of lock files and thought we were leaking them. I've never heard anyone report an actual functional or performance problem as a result of the lock files. I don't think we should "fix" this until someone reports that it's actually broken. Especially because previous attempts have all resulted in very real bugs that did break people. Maybe we should have oslo.concurrency drop a file named _README (or something else likely to sort first in the file listing) into the configured lock_path that explains why the files are there and the proper way to deal with them.

Thanks

Le lun. 30 sept. 2019 à 03:35, Rikimaru Honjo <honjo.rikimaru@ntt-tx.co.jp <mailto:honjo.rikimaru@ntt-tx.co.jp>> a écrit :

On 2019/09/28 1:44, Ben Nemec wrote: > > > On 9/23/19 11:42 PM, Rikimaru Honjo wrote: >> Hi Eric, >> >> On 2019/09/20 23:10, Eric Harney wrote: >>> On 9/20/19 1:52 AM, Rikimaru Honjo wrote: >>>> Hi, >>>> >>>> I'm using Queens cinder with the following setting. >>>> >>>> --------------------------------- >>>> [coordination] >>>> backend_url = file://$state_path >>>> --------------------------------- >>>> >>>> As a result, the files like the following were remained under the state path after some operations.[1] >>>> >>>> cinder-63dacb3d-bd4d-42bb-88fe-6e4180164765-delete_volume >>>> cinder-32c426af-82b4-41de-b637-7d76fed69e83-delete_snapshot >>>> >>>> In my understanding, these are lock-files created for synchronization by tooz. >>>> But, these lock-files were not deleted after finishing operations. >>>> Is this behaviour correct? >>>> >>>> [1] >>>> e.g. Delete volume, Delete snapshot >>> >>> This is a known bug that's described here: >>> >>> https://github.com/harlowja/fasteners/issues/26 >>> >>> (The fasteners library is used by tooz, which is used by Cinder for managing these lock files.) >>> >>> There's an old Cinder bug for it here: >>> https://bugs.launchpad.net/cinder/+bug/1432387 >>> >>> but that's marked as "Won't Fix" because Cinder needs it to be fixed in the underlying libraries. >> Thank you for your explanation. >> I understood the state. >> >> But, I have one more question. >> Can I think this bug doesn't affect synchronization? > > It does not. In fact, it's important to not remove lock files while a service is running or you can end up with synchronization issues. > > To clean up the leftover lock files, we generally recommend clearing the lock_path for each service on reboot before the services have started.

Thank you for your information. I think that I understood this issue completely.

Best Regards,

>> >> Best regards, >> >>> Thanks, >>> Eric >>> >> >

-- _/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/ Rikimaru Honjo E-mail:honjo.rikimaru@ntt-tx.co.jp <mailto:E-mail%3Ahonjo.rikimaru@ntt-tx.co.jp>

-- Hervé Beraud Senior Software Engineer Red Hat - Openstack Oslo irc: hberaud -----BEGIN PGP SIGNATURE-----

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On 10/15/19 10:24 AM, Cédric Jeanneret wrote:

On 10/15/19 4:47 PM, Ben Nemec wrote:

...

On 10/15/19 7:48 AM, Herve Beraud wrote:

...

I proposed some patches through heat templates and puppet-cinder to remove lock files older than 1 week and avoid file system growing.

This is a solution based on a cron job, to fix that on stable branches, in a second time I'll help the fasteners project to fix the root cause by reviewing and testing the proposed patch (lock based on file offset). In next versions I hope we will use a patched fasteners and so we could drop the cron based solution.

Please can you give /reviews/feedbacks: - https://review.opendev.org/688413 - https://review.opendev.org/688414 - https://review.opendev.org/688415

I'm rather hesitant to recommend this. It looks like the change is only removing the -delete lock files, which are a fraction of the total lock files created by Cinder, and I don't particularly want to encourage people to start monkeying with the lock files while a service is running. Even with this limited set of deletions, I think we need a Cinder person to look and verify that we aren't making bad assumptions about how the locks are used.

I'm also not that happy with the cron way - but apparently it might create some issues in some setup with the current way things are done: - inodes aren't infinit on ext* FS (ext3, ext4, blah) - see bellow for context - perfs might be bad (see bellow for context)

So one way or another, cleanup is needed.

...

In essence, I don't think this is going to meaningfully reduce the amount of leftover lock files and it sets a bad precedent for how to handle them.

The filter is strict - on purpose, to address this specific issue. Of course, we might want to loosen it, but... do we really want that? IF we're to go with the cron thingy of course. Some more thinking is needed I guess.

...

Personally, I'd rather see a boot-time service added for each OpenStack service that goes out and wipes the lock file directory before starting the service.

Well.... former sysops here: don't count on regular reboot - once a year is a fair average - and it's usually due to some power cut... Sad world, I know ;). So a "boot-time cleanup" will help. A little. And wouldn't hurt anyway. So +1 for that idea, but I wouldn't rely only on it. And there might be some issues (see bellow)

I understand that it doesn't happen regularly, but it's the easiest to automate safe time to clean locks. It can also be done when the service is down for maintenance, but even then you need to be careful because if you wipe the cinder locks when cinder-volume gets restarted, but cinder-scheduler is still running you might wipe an in-use lock. I don't know if that specific scenario is possible, but the point is that any process that could hold a lock needs to be down before you clear the lock directory. Since most OpenStack services have multiple separate OS services running that complicates the process.

...

On a more general note, I'm going to challenge the assertion that "Customer file system growing slowly and so customer risk to facing some issues to file system usage after a long period." I have yet to hear an actual bug report from the leftover lock files. Every time this comes up it's because someone noticed a lot of lock files and thought we were leaking them. I've never heard anyone report an actual functional or performance problem as a result of the lock files. I don't think we should "fix" this until someone reports that it's actually broken. Especially because previous attempts have all resulted in very real bugs that did break people.

I'm not on your side here. Waiting to get a fire before thinking about correction and counter-measures isn't good. Since we know there's an issue, and that, eventually, it might be a really big one, it would be good to address it before it explodes in our face.

If you have a solution that fixes the problem without introducing concurrency problems then I'm all ears. :-) Until then, I'm not comfortable fixing a hypothetical problem by creating very real new problems.

The disk *space* is probably not the issue. File with 1k, on a couple of gigas, it's good. But there are other concerns:

- inodes. Yes, we're supposed to get things on XFS, and that dude doesn't have inodes. But some ops might want to rely on the good(?) old ext3, or ext4. There, we might get some issues, and pretty quickly depending on the speed of lock creation (so, linked to cinder actions in this case). Or it might be some NFS with an ext4 FS.

- rm limits: you probably never ever hit "rm argument list limit". But it does exist, and I did hit it (like 15 years ago - maybe it's sorted out, but I have some doubts). This means that rm will NOT be able to cope with the directory content after a certain amount (which is huge, right, but still... we're talking about some long-lasting process filling a directory). Of course, "find" might be the right tool in such case, but it will take a long, long time to delete (thinking about the "boot-time cleanup proposal" for instance). > - performances: it might impact the system, for instance if one has some backup process running and wanting to eat the /var/lib/cinder directory: if the op doesn't know about this issue, they might get some surprises with long, long, loooong running backups. With a target on some ext4 - hello Inodes!

Sure, but these are all still theoretical problems. I've _never_ heard of anyone running into them, and we have some pretty big OpenStack deployments in the wild. I feel like at one point I did the math to figure out what it would take to hit an inode limit because of lock files, and it was fairly absurd. Like you would have to leave a deployment running for a decade under heavy use to actually get there. I don't still have those numbers handy, but it might be a useful exercise to look at that again. And this reminds me of another thing that has been suggested in the past to address the lock file cleanup issue (we should really write all of this down if we haven't already...), which is to put them on tmpfs. That way they get cleared automatically on reboot and you don't have to manage anything. Locks don't persist over reboots anyway so it doesn't matter that it's on volatile storage. The whole file thing is actually a consequence of Linux IPC being complete garbage, not because we want persistent storage of locks.

Sooo... yeah. I think this issue should be addressed. Really. But I +1 the fact that it should be done "the right way", whatever it is. The "cron" might be the wrong one. Or not. We need some more feedbacks on that :).

Patches welcome. But fair warning: This problem is a lot harder than it looks on the surface. Many solutions have been proposed over the years, all of them were worse than what we have now.

...

Maybe we should have oslo.concurrency drop a file named _README (or something else likely to sort first in the file listing) into the configured lock_path that explains why the files are there and the proper way to deal with them.

Hmmm... who reads README anyway? Like, really. Better getting some cleanup un place to avoid questions ;).

If it heads off even one of these threads that happen every few months then it will have been worth it. :-D

Cheers,

C.

...

...

Thanks

Le lun. 30 sept. 2019 à 03:35, Rikimaru Honjo <honjo.rikimaru@ntt-tx.co.jp <mailto:honjo.rikimaru@ntt-tx.co.jp>> a écrit :

    On 2019/09/28 1:44, Ben Nemec wrote:      >      >      > On 9/23/19 11:42 PM, Rikimaru Honjo wrote:      >> Hi Eric,      >>      >> On 2019/09/20 23:10, Eric Harney wrote:      >>> On 9/20/19 1:52 AM, Rikimaru Honjo wrote:      >>>> Hi,      >>>>      >>>> I'm using Queens cinder with the following setting.      >>>>      >>>> ---------------------------------      >>>> [coordination]      >>>> backend_url = file://$state_path      >>>> ---------------------------------      >>>>      >>>> As a result, the files like the following were remained under     the state path after some operations.[1]      >>>>      >>>> cinder-63dacb3d-bd4d-42bb-88fe-6e4180164765-delete_volume      >>>> cinder-32c426af-82b4-41de-b637-7d76fed69e83-delete_snapshot      >>>>      >>>> In my understanding, these are lock-files created for     synchronization by tooz.      >>>> But, these lock-files were not deleted after finishing operations.      >>>> Is this behaviour correct?      >>>>      >>>> [1]      >>>> e.g. Delete volume, Delete snapshot      >>>      >>> This is a known bug that's described here:      >>>      >>> https://github.com/harlowja/fasteners/issues/26      >>>      >>> (The fasteners library is used by tooz, which is used by Cinder     for managing these lock files.)      >>>      >>> There's an old Cinder bug for it here:      >>> https://bugs.launchpad.net/cinder/+bug/1432387      >>>      >>> but that's marked as "Won't Fix" because Cinder needs it to be     fixed in the underlying libraries.      >> Thank you for your explanation.      >> I understood the state.      >>      >> But, I have one more question.      >> Can I think this bug doesn't affect synchronization?      >      > It does not. In fact, it's important to not remove lock files     while a service is running or you can end up with synchronization     issues.      >      > To clean up the leftover lock files, we generally recommend     clearing the lock_path for each service on reboot before the     services have started.

    Thank you for your information.     I think that I understood this issue completely.

    Best Regards,

     >>      >> Best regards,      >>      >>> Thanks,      >>> Eric      >>>      >>      >

    --     _/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/     Rikimaru Honjo     E-mail:honjo.rikimaru@ntt-tx.co.jp     <mailto:E-mail%3Ahonjo.rikimaru@ntt-tx.co.jp>

-- Hervé Beraud Senior Software Engineer Red Hat - Openstack Oslo irc: hberaud -----BEGIN PGP SIGNATURE-----

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On 10/15/19 10:41 AM, Herve Beraud wrote:

Le mar. 15 oct. 2019 à 16:48, Ben Nemec <openstack@nemebean.com <mailto:openstack@nemebean.com>> a écrit :

On 10/15/19 7:48 AM, Herve Beraud wrote: > I proposed some patches through heat templates and puppet-cinder to > remove lock files older than 1 week and avoid file system growing. > > This is a solution based on a cron job, to fix that on stable branches, > in a second time I'll help the fasteners project to fix the root cause > by reviewing and testing the proposed patch (lock based on file offset). > In next versions I hope we will use a patched fasteners and so we could > drop the cron based solution. > > Please can you give /reviews/feedbacks: > - https://review.opendev.org/688413 > - https://review.opendev.org/688414 > - https://review.opendev.org/688415

I'm rather hesitant to recommend this. It looks like the change is only removing the -delete lock files, which are a fraction of the total lock files created by Cinder, and I don't particularly want to encourage people to start monkeying with the lock files while a service is running. Even with this limited set of deletions, I think we need a Cinder person to look and verify that we aren't making bad assumptions about how the locks are used.

Yes these changes should be validated by the cinder team. I chosen this approach to allow use to fix that on stable branches too, and to avoid to introduce a non backportable new feature.

In essence, I don't think this is going to meaningfully reduce the amount of leftover lock files and it sets a bad precedent for how to handle them.

Personally, I'd rather see a boot-time service added for each OpenStack service that goes out and wipes the lock file directory before starting the service.

I agree it can be an alternative to the proposed changes. I guess it's related to some sort of puppet code too, I'm right? (the boot-time service)

That's probably how you'd implement it in TripleO. Or maybe Ansible now. Best to check with the TripleO team on that since my knowledge is quite out of date on that project now.

On a more general note, I'm going to challenge the assertion that "Customer file system growing slowly and so customer risk to facing some issues to file system usage after a long period." I have yet to hear an actual bug report from the leftover lock files. Every time this comes up it's because someone noticed a lot of lock files and thought we were leaking them. I've never heard anyone report an actual functional or performance problem as a result of the lock files. I don't think we should "fix" this until someone reports that it's actually broken. Especially because previous attempts have all resulted in very real bugs that did break people.

Yes I agreee it's more an assumption than a reality, I never seen anybody report a disk usage issue or things like this due to leftover lock files.

Maybe we should have oslo.concurrency drop a file named _README (or something else likely to sort first in the file listing) into the configured lock_path that explains why the files are there and the proper way to deal with them.

Good idea.

Anyway, even if nobody facing a file system issue related to files leftover, I think it's not a good thing to lets grow a FS, and we need to try to address it to prevent potential file system issues related to disk usage and lock files, but in a secure way to avoid to introduce race conditions with cinder.

Cinder people need to confirm that my proposed changes can fit well with cinder's mechanismes or choose a better approach.

I'm opposed in general to external solutions. If lock files are to be cleaned up, it needs to happen either when the service isn't running so there's no chance of deleting an in-use lock, or it needs to be done by the service itself when it knows that it is done with the lock. Any fixes outside the service run the risk of drifting from the implementation if, for example, Cinder made a change to its locking semantics such that locks you could safely remove previously no longer could be. I believe Neutron implements lock file cleanup using [0], which is really the only way runtime lock cleanup should be done IMHO. 0: https://github.com/openstack/oslo.concurrency/blob/85c341aced7b181724b68c9d8...

> > Thanks > > > Le lun. 30 sept. 2019 à 03:35, Rikimaru Honjo > <honjo.rikimaru@ntt-tx.co.jp <mailto:honjo.rikimaru@ntt-tx.co.jp> <mailto:honjo.rikimaru@ntt-tx.co.jp <mailto:honjo.rikimaru@ntt-tx.co.jp>>> a écrit : > >     On 2019/09/28 1:44, Ben Nemec wrote: >      > >      > >      > On 9/23/19 11:42 PM, Rikimaru Honjo wrote: >      >> Hi Eric, >      >> >      >> On 2019/09/20 23:10, Eric Harney wrote: >      >>> On 9/20/19 1:52 AM, Rikimaru Honjo wrote: >      >>>> Hi, >      >>>> >      >>>> I'm using Queens cinder with the following setting. >      >>>> >      >>>> --------------------------------- >      >>>> [coordination] >      >>>> backend_url = file://$state_path >      >>>> --------------------------------- >      >>>> >      >>>> As a result, the files like the following were remained under >     the state path after some operations.[1] >      >>>> >      >>>> cinder-63dacb3d-bd4d-42bb-88fe-6e4180164765-delete_volume >      >>>> cinder-32c426af-82b4-41de-b637-7d76fed69e83-delete_snapshot >      >>>> >      >>>> In my understanding, these are lock-files created for >     synchronization by tooz. >      >>>> But, these lock-files were not deleted after finishing operations. >      >>>> Is this behaviour correct? >      >>>> >      >>>> [1] >      >>>> e.g. Delete volume, Delete snapshot >      >>> >      >>> This is a known bug that's described here: >      >>> >      >>> https://github.com/harlowja/fasteners/issues/26 >      >>> >      >>> (The fasteners library is used by tooz, which is used by Cinder >     for managing these lock files.) >      >>> >      >>> There's an old Cinder bug for it here: >      >>> https://bugs.launchpad.net/cinder/+bug/1432387 >      >>> >      >>> but that's marked as "Won't Fix" because Cinder needs it to be >     fixed in the underlying libraries. >      >> Thank you for your explanation. >      >> I understood the state. >      >> >      >> But, I have one more question. >      >> Can I think this bug doesn't affect synchronization? >      > >      > It does not. In fact, it's important to not remove lock files >     while a service is running or you can end up with synchronization >     issues. >      > >      > To clean up the leftover lock files, we generally recommend >     clearing the lock_path for each service on reboot before the >     services have started. > >     Thank you for your information. >     I think that I understood this issue completely. > >     Best Regards, > > >      >> >      >> Best regards, >      >> >      >>> Thanks, >      >>> Eric >      >>> >      >> >      > > >     -- >     _/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/ >     Rikimaru Honjo > E-mail:honjo.rikimaru@ntt-tx.co.jp <mailto:E-mail%3Ahonjo.rikimaru@ntt-tx.co.jp> >     <mailto:E-mail%3Ahonjo.rikimaru@ntt-tx.co.jp <mailto:E-mail%253Ahonjo.rikimaru@ntt-tx.co.jp>> > > > > > -- > Hervé Beraud > Senior Software Engineer > Red Hat - Openstack Oslo > irc: hberaud > -----BEGIN PGP SIGNATURE----- > > wsFcBAABCAAQBQJb4AwCCRAHwXRBNkGNegAALSkQAHrotwCiL3VMwDR0vcja10Q+ > Kf31yCutl5bAlS7tOKpPQ9XN4oC0ZSThyNNFVrg8ail0SczHXsC4rOrsPblgGRN+ > RQLoCm2eO1AkB0ubCYLaq0XqSaO+Uk81QxAPkyPCEGT6SRxXr2lhADK0T86kBnMP > F8RvGolu3EFjlqCVgeOZaR51PqwUlEhZXZuuNKrWZXg/oRiY4811GmnvzmUhgK5G > 5+f8mUg74hfjDbR2VhjTeaLKp0PhskjOIKY3vqHXofLuaqFDD+WrAy/NgDGvN22g > glGfj472T3xyHnUzM8ILgAGSghfzZF5Skj2qEeci9cB6K3Hm3osj+PbvfsXE/7Kw > m/xtm+FjnaywZEv54uCmVIzQsRIm1qJscu20Qw6Q0UiPpDFqD7O6tWSRKdX11UTZ > hwVQTMh9AKQDBEh2W9nnFi9kzSSNu4OQ1dRMcYHWfd9BEkccezxHwUM4Xyov5Fe0 > qnbfzTB1tYkjU78loMWFaLa00ftSxP/DtQ//iYVyfVNfcCwfDszXLOqlkvGmY1/Y > F1ON0ONekDZkGJsDoS6QdiUSn8RZ2mHArGEWMV00EV5DCIbCXRvywXV43ckx8Z+3 > B8qUJhBqJ8RS2F+vTs3DTaXqcktgJ4UkhYC2c1gImcPRyGrK9VY0sCT+1iA+wp/O > v6rDpkeNksZ9fFSyoY2o > =ECSj > -----END PGP SIGNATURE----- >

-- Hervé Beraud Senior Software Engineer Red Hat - Openstack Oslo irc: hberaud -----BEGIN PGP SIGNATURE-----

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Thanks Ben for your feedbacks. I already tried to follow the `remove_external_lock_file` few months ago, but unfortunately, I don't think we can goes like this with Cinder... As Gorka has explained to me few months ago:

Those are not the only type of locks we use in Cinder. Those are the ones we call "Global locks" and use TooZ so the DLM can be configured for Cinder Active-Active.

We also use Oslo's synchronized locks.

More information is available in the Cinder HA dev ref I wrote last year. It has a section dedicated to the topic of mutual exclusion and the 4 types we currently have in Cinder [1]:

- Database locking using resource states. - Process locks. - Node locks. - Global locks.

As for calling the remove_external_lock_file_with_prefix directly on delete, I don't think that's something we can do, as the locks may still be in use. Example:

- Start deleting volume -> get lock - Try to clone volume -> wait for lock - Finish deleting volume -> release and delete lock - Cloning recreates the lock when acquiring it - Cloning fails because the volume no longer exists but leaves the lock

So the Cinder workflow and mechanisms seems to definitively forbid to us the possibility to use the remove features of oslo.concurrency... Also like discussed on the review (https://review.opendev.org/#/c/688413), this issue can't be fixed in the underlying libraries, and I think that if we want to fix that on stable branches then Cinder need to address it directly by adding some piece of code who will be triggered if needed and in a safely manner, in other words, only Cinder can really address it and remove safely these file. See the discussion extract on the review ( https://review.opendev.org/#/c/688413):

Thanks Gorka for your feedback, then in view of all the discussions about this topic I suppose only Cinder can really address it safely on stable branches.

...

It is not a safe assumption that *-delete_volume file locks can be removed just because they have not been used in a couple of days. A new volume clone could come in that would use it and then we could have a race condition if the cron job was running.

The only way to be sure that it can be removed is checking in the Cinder DB and making sure that the volume has been deleted or it doesn't even exist (DB has been purged).

Same thing with detach_volume, delete_snapshot, and those that are directly volume ids locks.

I definitely think that it can't be fixed in the underlying libraries like Eric has suggested [1], indeed, as you has explained only Cinder can know if a lock file can be removed safely.

...

In my opinion the fix should be done in fasteners, or we should add code in Cinder that cleans up all locks related to a volume or snapshot when this one is deleted.

I agree the most better solution is to fix the root cause and so to fix fasteners, but I don't think it's can be backported to stable branches because we will need to bump a requirement version on stable branche in this case and also because it'll introduce new features, so I guess Cinder need to add some code to remove these files and possibly backport it to stable branches.

[1] http://lists.openstack.org/pipermail/openstack-discuss/2019-September/009563...

The Fasteners fix IMHO can only be used by future versions of openstack, due to the version bump and due to the new features added. I think that it could be available only from the ussuri or future cycle like V. The main goal of the cron approach was to definitively avoid to unearth this topic each 6 months, try to address it on stable branches, and try to take care of the file system usage even if it's a theoretical issue, but by getting feedbacks from the Cinder team and their warnings I don't think that this track is still followable. Definitely, this is not an oslo.concurrency bug. Anyway your proposed "Administrator Guide" is a must to have, to track things in one place, inform users and avoid to spend time to explain the same things again and again about this topic... so it's worth-it. I'll review it and propose my related knowledge on this topic. oslo.concurrency can't address this safely because we risk to introduce race conditions and worse situations than the leftover lock files. So, due to all these elements, only cinder can address it for the moment and for fix that on stable branches too. Le mer. 16 oct. 2019 à 00:15, Ben Nemec <openstack@nemebean.com> a écrit :

In the interest of not having to start this discussion from scratch every time, I've done a bit of a brain dump into https://review.opendev.org/#/c/688825/ that covers why things are the way they are and what we recommend people do about it. Please take a look and let me know if you see any issues with it.

Thanks.

-Ben

-- Hervé Beraud Senior Software Engineer Red Hat - Openstack Oslo irc: hberaud -----BEGIN PGP SIGNATURE----- wsFcBAABCAAQBQJb4AwCCRAHwXRBNkGNegAALSkQAHrotwCiL3VMwDR0vcja10Q+ Kf31yCutl5bAlS7tOKpPQ9XN4oC0ZSThyNNFVrg8ail0SczHXsC4rOrsPblgGRN+ RQLoCm2eO1AkB0ubCYLaq0XqSaO+Uk81QxAPkyPCEGT6SRxXr2lhADK0T86kBnMP F8RvGolu3EFjlqCVgeOZaR51PqwUlEhZXZuuNKrWZXg/oRiY4811GmnvzmUhgK5G 5+f8mUg74hfjDbR2VhjTeaLKp0PhskjOIKY3vqHXofLuaqFDD+WrAy/NgDGvN22g glGfj472T3xyHnUzM8ILgAGSghfzZF5Skj2qEeci9cB6K3Hm3osj+PbvfsXE/7Kw m/xtm+FjnaywZEv54uCmVIzQsRIm1qJscu20Qw6Q0UiPpDFqD7O6tWSRKdX11UTZ hwVQTMh9AKQDBEh2W9nnFi9kzSSNu4OQ1dRMcYHWfd9BEkccezxHwUM4Xyov5Fe0 qnbfzTB1tYkjU78loMWFaLa00ftSxP/DtQ//iYVyfVNfcCwfDszXLOqlkvGmY1/Y F1ON0ONekDZkGJsDoS6QdiUSn8RZ2mHArGEWMV00EV5DCIbCXRvywXV43ckx8Z+3 B8qUJhBqJ8RS2F+vTs3DTaXqcktgJ4UkhYC2c1gImcPRyGrK9VY0sCT+1iA+wp/O v6rDpkeNksZ9fFSyoY2o =ECSj -----END PGP SIGNATURE-----

...

Hi,

I've given it some more thought, and I am now on the side of those that argue that "something imperfect" is better than what we currently have, so maybe we can reach some sort of compromise doing the following:

- Cleanup locks directory on node start

Didn't we determine this was not safe since multiple services can be configured to use the same lock directory? In fact, that was the recommended configuration I think when running Cinder and Nova services on the same node so os-brick locks would actually work right (or something like that, it was awhile ago now).

- Remove locks on delete volume/snapshot operation - Remove locks on missing source on create volume (volume/snapshot)

+1