cuse: Implement hot-unload
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Authored by christos on Fri, Sep 25, 11:50 AM.

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Reviewers

markj
emaste
kib

Commits

rGd38ef1aca969: cuse: Implement hot-unload

Summary

cuse_kern_uninit() can hang on destroy_dev(), because of threads
sleeping in CUSE_IOCTL_GET_COMMAND, so wake them up before calling
destroy_dev(). Also do not allow threads to go back to sleep if the
is_closing flag has been set.

MFC after: 1 week
Sponsored by: The FreeBSD Foundation

Test Plan

Tested with virtual_oss:

root@freebsd:~ # service virtual_oss onestart
Starting virtual_oss config: dsp: hw.snd.basename_clone: 1 -> 0
done
root@freebsd:~ # ls /dev/dsp
/dev/dsp        /dev/dsp.dummy  /dev/dsp.loop   /dev/dsp0
root@freebsd:~ # kldunload cuse
root@freebsd:~ # ls /dev/dsp
/dev/dsp.dummy  /dev/dsp0
root@freebsd:~ # service virtual_oss onestop
Stopping virtual_oss config: dsp: done

Diff Detail

Repository

rG FreeBSD src repository

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Build Status

Buildable 77318
Build 74201: arc lint + arc unit

Event Timeline

christos created this revision.Fri, Sep 25, 11:50 AM

Herald added a subscriber: imp. · View Herald TranscriptFri, Sep 25, 11:50 AM

christos requested review of this revision.Fri, Sep 25, 11:50 AM

Harbormaster completed remote builds in B77318: Diff 187667.Fri, Sep 25, 11:50 AM

christos edited the test plan for this revision. (Show Details)Fri, Sep 25, 11:52 AM

We have d_purge cdevsw method. It is invoked by destroy_dev(9) when it observes threads inside cdevsw methods, to release the sleep. Would it be useful for your purpose there?

In D60022#1377269, @kib wrote:

We have d_purge cdevsw method. It is invoked by destroy_dev(9) when it observes threads inside cdevsw methods, to release the sleep. Would it be useful for your purpose there?

I see only one use of d_purge in the tree. What I want is to wake up the server cv that's sleeping in CUSE_IOCTL_GET_COMMAND and set is_closing. I guess d_purge should be good, or is there something that might bite us?

In D60022#1377546, @christos wrote:

In D60022#1377269, @kib wrote:

We have d_purge cdevsw method. It is invoked by destroy_dev(9) when it observes threads inside cdevsw methods, to release the sleep. Would it be useful for your purpose there?

I see only one use of d_purge in the tree. What I want is to wake up the server cv that's sleeping in CUSE_IOCTL_GET_COMMAND and set is_closing. I guess d_purge should be good, or is there something that might bite us?

Well, d_purge intent was specifically to expedite threads out of cdevsw methods on destroy_dev(). It is relatively delicate option so it was only used by the core tty infra AFAIR. So it should be good. I do not know of something that could bite (in advance).