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Date:      Tue, 24 Mar 2020 23:15:12 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 244878] Kernel panic due to spin lock held too long
Message-ID:  <bug-244878-227-v8qGqVFtFD@https.bugs.freebsd.org/bugzilla/>
In-Reply-To: <bug-244878-227@https.bugs.freebsd.org/bugzilla/>
References:  <bug-244878-227@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D244878

Jason A. Harmening <jah@FreeBSD.org> changed:

           What    |Removed                     |Added
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                 CC|                            |jah@FreeBSD.org

--- Comment #3 from Jason A. Harmening <jah@FreeBSD.org> ---
Not a lot to go on from the backtrace.   One thing that can cause this pani=
c is
if a thread calls smp_rendezvous_cpus() with local interrupts disabled: if
another thread holds smp_ipi_mtx and is trying to IPI the first thread's CP=
U,
the two threads can livelock.

It doesn't look like the timer callout+in6 route expiration path that panic=
ked
should ever call smp_rendezvous_cpus() with interrupts disabled, but I think
it's also possible that this thread could have been the victim of two other
threads that were livelocked.

r357308 added a check to HEAD (INVARIANTS kernels only) that panics if a th=
read
enters smp_rendezvous_cpus() with interrupts disabled.  If this is at all
reproducible, it might be worth trying a kernel with that check backported.

Also worth noting: in6_mtutimo() was completely removed from HEAD in 355888.

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