Date: Wed, 15 Dec 2004 11:59:34 -0800 From: Nate Lawson <nate@root.org> To: John Baldwin <jhb@FreeBSD.org> Cc: Kris Kennaway <kris@obsecurity.org> Subject: Re: cvs commit: src/sys/i386/i386 vm_machdep.c Message-ID: <41C097A6.8070305@root.org> In-Reply-To: <200412142148.48019.jhb@FreeBSD.org> References: <200411300618.iAU6IkQX065609@repoman.freebsd.org> <41BF6F44.2090407@root.org> <20041215001034.GA60875@xor.obsecurity.org> <200412142148.48019.jhb@FreeBSD.org>
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John Baldwin wrote: > On Tuesday 14 December 2004 07:10 pm, Kris Kennaway wrote: > >>On Tue, Dec 14, 2004 at 02:55:00PM -0800, Nate Lawson wrote: >> >>>>Erm, well, that's not always easy since sometimes when you panic you >>>>can't talk to the other CPUs for whatever reason. Putting back the >>>>proxy reset doesn't hurt for now but does restore functionality in at >>>>least some cases. I'd rather have that then certain hard panics not >>>>get into ddb because we couldn't get onto the BSP to run ddb. >>> >>>Perhaps you could give me some pointers on what is counted on to be >>>working when panic() is called? I can't come up with a situation where >>>the proxy code couldn't be used upon entry to ddb. If there were any >>>cases like this, the proxy code wouldn't work for cpu_reset() either. >>>Also, in such a case, it's hard to see how ddb could be usable since it >>>tries to stop other processors, which requires similar code to the proxy. >>> >>>Or in other words, if you have enough capability to call panic() or >>>break to ddb, then you have enough resources to do an IPI and get onto >>>the BSP. >> >>NB: DDB often isn't usable on SMP machines thesedays, and will hang >>when a panic tries to enter it. > > > Try debug.kdb.stop_cpus=0 (sysctl and tunable) to prevent KDB from trying to > stop the other CPUs. Another possible fix that ups@ has talked about is > changing IPI_STOP to use an NMI rather than a vector (you can send NMI IPIs > via the local APIC) so that IPI_STOP is more reliable. That would be excellent. If that was implemented, would it be acceptable then to stop the cpus while entering ddb or on panic? I think it would be reliable enough to always do this. -- Nate
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