Differential D42460

reboot: Avoid unlocking Giant if the scheduler is stopped
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Authored by markj on Nov 3 2023, 8:48 PM.

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rG8da1c3715139: reboot: Avoid unlocking Giant if the scheduler is stopped
rGdeacab756026: reboot: Avoid unlocking Giant if the scheduler is stopped

Summary

When the scheduler is stopped, mtx_unlock() turns into a no-op, so the
loop

    while (mtx_owned(&Giant))
	    mtx_unlock(&Giant);

runs forever if the calling thread has Giant locked.

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rG FreeBSD src repository

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Event Timeline

markj created this revision.Nov 3 2023, 8:48 PM

Herald added a subscriber: imp. · View Herald TranscriptNov 3 2023, 8:48 PM

markj requested review of this revision.Nov 3 2023, 8:48 PM

Harbormaster completed remote builds in B54273: Diff 129698.Nov 3 2023, 8:48 PM

No objection, but I wonder why we loop at all.

This revision is now accepted and ready to land.Nov 4 2023, 2:44 PM

In D42460#968986, @mhorne wrote:

No objection, but I wonder why we loop at all.

Giant is recursive, so it could in principle be held multiple times by the same thread.

Closed by commit rGdeacab756026: reboot: Avoid unlocking Giant if the scheduler is stopped (authored by markj). · Explain WhyNov 4 2023, 2:49 PM

This revision was automatically updated to reflect the committed changes.

markj added a commit: rGdeacab756026: reboot: Avoid unlocking Giant if the scheduler is stopped.

I thought I'd hit accept yesterday this is fine. Crashes are super weird. I can't think of any other place we do this.. Giant really is special.

markj added a commit: rG8da1c3715139: reboot: Avoid unlocking Giant if the scheduler is stopped.Nov 7 2023, 12:24 AM

Revision Contents
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Path

Size

sys/

kern/

kern_shutdown.c

2 lines

Diff 129716

sys/kern/kern_shutdown.c

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