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Differential D22548

devfs: introduce a per-dev lock to protect ->si_devsw
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Authored by mjg on Nov 25 2019, 4:52 PM.
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rS355228: devfs: introduce a per-dev lock to protect ->si_devsw
Summary

This allows bumping threadcount without taking the global devmtx lock.

markj reports it eliminates contention on said lock on a sample system with 32 instances of bhyve. Also it went went through stress testing while hosting syzkaller. No issues found.

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Event Timeline

mjg created this revision.Nov 25 2019, 4:52 PM
Herald added a subscriber: imp. · View Herald TranscriptNov 25 2019, 4:52 PM
Harbormaster completed remote builds in B27760: Diff 64855.Nov 25 2019, 4:52 PM
kib added a comment.Nov 25 2019, 4:58 PM

This absolutely requires a bump for D_VERSION.
May be add explicit order between devmtx and si_threadlock to the witness static table.

mjg updated this revision to Diff 64857.Nov 25 2019, 5:15 PM
  • bump D_VERSION
  • annotate the lock in witness
kib added inline comments.Nov 25 2019, 9:03 PM
sys/sys/conf.h
174 ↗(On Diff #64857)

After closer look, can we avoid this bump ? si_threadlock is used (should be used) only be devfs internals, so if you move the lock into cdev_priv it should still work.

mjg updated this revision to Diff 64923.Nov 27 2019, 1:31 AM
  • move the lock to cdev_privdata
kib accepted this revision.Nov 27 2019, 11:25 AM

Except for the headers pollution, I am fine with the change.

sys/fs/devfs/devfs_int.h
43

Is that needed ? Even if it is, devfs_int.h is included in 5 or 6 files at all, so it is easy to arrange sys/mutex.h before it in .c files.

This revision is now accepted and ready to land.Nov 27 2019, 11:25 AM
evgueni.gavrilov_itglobal.com added a subscriber: evgueni.gavrilov_itglobal.com.Nov 27 2019, 1:22 PM
mjg updated this revision to Diff 64939.Nov 27 2019, 3:34 PM
  • drop _lock.h and _mtx.h

I included them towards self-contianment of the header file. universe MAKE_JUST_KERNELS builds just fine (except for powerpc* which were note tested)

This revision now requires review to proceed.Nov 27 2019, 3:34 PM
kib accepted this revision.Nov 27 2019, 4:00 PM
This revision is now accepted and ready to land.Nov 27 2019, 4:00 PM
Closed by commit rS355228: devfs: introduce a per-dev lock to protect ->si_devsw (authored by mjg). · Explain WhyNov 30 2019, 4:46 PM
This revision was automatically updated to reflect the committed changes.
mjg added a commit: rS355228: devfs: introduce a per-dev lock to protect ->si_devsw.

Revision Contents
Changeset List

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sys/
fs/
devfs/
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2 lines
kern/
20 lines
1 line

Diff 64939

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sys/fs/devfs/devfs_devs.c

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sys/fs/devfs/devfs_int.h

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sys/kern/kern_conf.c

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sys/kern/subr_witness.c

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