Date: Fri, 21 Aug 2015 10:19:47 -0500 From: Eric van Gyzen <vangyzen@FreeBSD.org> To: Ryan Stone <rysto32@gmail.com>, Adrian Chadd <adrian@freebsd.org> Cc: freebsd-current <freebsd-current@freebsd.org>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org>, Scott Long <scottl@freebsd.org>, Konstantin Belousov <kib@freebsd.org> Subject: Re: freebsd-head: suddenly NMI panics lead to ddb being unable to stop CPUs? Message-ID: <55D74193.4020008@FreeBSD.org> In-Reply-To: <CAFMmRNw6tWMQ-pfXzSpEM7kRgKafB9KnK-oUhWw2_E-P91drLw@mail.gmail.com> References: <CAJ-VmomvqULP--v47qKJisQkf8VQNvxEhXK=HXEtv9MuLz4D1g@mail.gmail.com> <CAFMmRNw6tWMQ-pfXzSpEM7kRgKafB9KnK-oUhWw2_E-P91drLw@mail.gmail.com>
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I mentioned this to Adrian, but I'll mention here for everyone else's benefit. Ryan is exactly right. There was a thread a while ago, with a proposed patch from Kostik: https://lists.freebsd.org/pipermail/freebsd-arch/2014-July/015584.html As I recall, Scott Long also ran into this a few months ago. It happens for any NMI: entering the debugger, a PCI Parity or System Error, a hardware watchdog timeout, and probably other sources I'm not remembering. Eric On 08/21/2015 09:23, Ryan Stone wrote: > I have seen similar behaviour before. The problem is that every CPU > receives an NMI concurrently. As I recall, one of them gets some kind of > pseudo-spinlock and tries to stop the other CPUs with an NMI. However, > because they are already in an NMI handler, they don't get the second NMI > and don't stop properly. > > The case that I saw actually had to do with a panic triggered by an NMI, > not entering the debugger, but I believe that both cases use > stop_cpus_hard() under the hood and have a similar issue. > > (I also recall seeing the exact situation that you describe while > originally developing SR-IOV on an alpha version of the Fortville hardware > and firmware with a very buggy SR-IOV implementation. I've never seen it > on ixgbe before, although I haven't used SR-IOV there very much at all) > > > On Thu, Aug 20, 2015 at 6:15 PM, Adrian Chadd <adrian@freebsd.org> wrote: > >> Hi! >> >> This has started happening on -HEAD recently. No, I don't have any >> more details yet than "recently." >> >> Whenever I get an NMI panic (and getting an NMI is a separate issue, >> sigh) I get a slew of "failed to stop cpu" messages, and all CPUs >> enter ddb. This is .. sub-optimal. Has anyone seen this? Does anyone >> have any ideas? >> >> >> -adrian
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