On 11/18/2014 05:39 PM, Benjamin Kaduk wrote:
On Tue, 18 Nov 2014, Ellis H. Wilson III wrote:
I'm observing the following two WITNESS LORs being thrown upon boot-up of 10.0
and I was tracking current, hoping they would go away by 10.1, but it seems
they persist as shown below.  I suspect this is because current is being built
with WITNESS on but also with SKIPSPIN on.  So these issues are unlikely to
show up for any devs but those who specifically enable WITNESS and disable
SKIPSPIN like myself.  At my work we would greatly like to do our debugging
with checking of spin-locking order included and panicing upon LOR detection.
That's not possible with these in existence.

However, I was under the impression that a kernel built with WITNESS and
without WITNESS_SKIPSPIN would panic on boot on the cnputs_mutx (see,
So, (1) I'm surprised you can boot it, and (2) that would explain why no
one else has been using it.

That's a very interesting thread. I've seen another where a fellow developer suggested just throwing on the WITNESS_SKIPSPIN flag to "solve" the issue. I can't say that I agree with the approach, but I understand. I'd be willing to tackle a bit of WITNESS massaging to help it be instructed about known false positives better, if that's desirable.

Why I'm able to boot however, is simple: I haven't enabled a full suite of debugging flags, KDB/DDB being the key ones that cause a panic to occur on a failure like the one I've seen. We originally were seeing the panic so WITNESS in its entirety was shut off. I was asked to try and get that back on-track, so to start I at least wanted to see how many LORs we were dealing with on boot. 2 is apparently that magic number, and maybe 3 if the cputs issue you refer to is still possible to be hit in the 10.1 wild.

If nobody has seen these before, I'll try and put together fixes for them. Please somebody speak up if you have seen them or have useful information for me to go on in my patches.


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