LinuxKPI: Allow spin_lock_irqsave to be called within a critical section
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Authored by wulf on Jan 13 2022, 11:48 PM.

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Reviewers

• hselasky
manu

Commits

rG02ea6033020e: LinuxKPI: Allow spin_lock_irqsave to be called within a critical section

Summary

with spinning on spin_trylock. dma-buf part of drm-kmod depends on this
property and absence of it support results in "mi_switch: switch in a
critical section" assertions [1][2].

[1] https://github.com/freebsd/drm-kmod/issues/116
[2] https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=261166

MFC after: 1 week

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rG FreeBSD src repository

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Event Timeline

wulf created this revision.Jan 13 2022, 11:48 PM

Herald added subscribers: linuxkpi, emaste, imp. · View Herald TranscriptJan 13 2022, 11:48 PM

wulf requested review of this revision.Jan 13 2022, 11:48 PM

Harbormaster completed remote builds in B43915: Diff 101436.Jan 13 2022, 11:48 PM

wulf added a child revision: D33888: LinuxKPI: Allow wake_up to be executed within a critical section.Jan 13 2022, 11:52 PM

grahamperrin added a subscriber: grahamperrin.Jan 14 2022, 12:30 AM

manu accepted this revision.Jan 14 2022, 6:28 AM

This revision is now accepted and ready to land.Jan 14 2022, 6:28 AM

• hselasky added inline comments.Jan 14 2022, 3:51 PM

sys/compat/linuxkpi/common/include/linux/spinlock.h
120	Is this a property of spin_lock_irqsave() only or should other spin_lock() functions be updated aswell?

wulf added inline comments.Jan 14 2022, 6:07 PM

sys/compat/linuxkpi/common/include/linux/spinlock.h
120	AFAIK no, they should not. Ordinary spin_lock() requires fully preemptible context at least on RT-kernels. See `PREEMPT_RT caveats` section of https://www.kernel.org/doc/html/latest/locking/locktypes.html May be some other spin_lock_XXX functions e.g. spin_lock_irqsave_nested() can be updated too, but I did not dig in to this direction.