[Bug 276587] ccp(4) causes 'sysctl -a' to hang when reading OID 'kern.geom.conftxt'

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=276587

--- Comment #5 from John Baldwin <jhb@FreeBSD.org> ---
A missed interrupt was the theory in the previous PR (and in that case the
theory was that it was possibly a hardware issue).  You can use kgdb on a live
system to investigate stack traces of sleeping threads and examine variables,
etc.  Just 'pkg install devel/gdb' and run 'kgdb' as root.  You can then use
normal GDB commands.  Each kernel thread is a thread in GDB in this mode.  That
said, there is probably not a stack to examine if ccp(4) is missing an
interrupt.  Instead, you would want to either see if ccp(4) maintains a
linked-list of pending operations or dump the descriptor rings to infer if
there are commands in flight.  Not sure if ccp has a counter for "in-flight"
requests (ccr(4) which ccp(4) is roughly based on does have such a counter).

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