Date: Fri, 12 Jun 2015 21:55:21 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Maksim Yevmenkin <maksim.yevmenkin@gmail.com> Cc: Andriy Gapon <avg@freebsd.org>, "current@freebsd.org" <current@freebsd.org> Subject: Re: obtaining a minidump from panic() called from NMI handler Message-ID: <20150612185521.GE2080@kib.kiev.ua> In-Reply-To: <CAFPOs6p5yTvdbJXPOKXuagZxj%2Bu-pE3kt5fsCWCpPVj4vktO%2Bg@mail.gmail.com> References: <CAFPOs6qsFZKMVzLEDL5X77H6s5LoTjsc4SkMWgR0D_P8RQG4YQ@mail.gmail.com> <557B1905.80307@FreeBSD.org> <CAFPOs6p5yTvdbJXPOKXuagZxj%2Bu-pE3kt5fsCWCpPVj4vktO%2Bg@mail.gmail.com>
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On Fri, Jun 12, 2015 at 11:49:01AM -0700, Maksim Yevmenkin wrote: > Andriy, > > >> i have a question about obtaining minidump as result of panic() being > >> called from nmi handler. basically, i have a way to trigger nmi, and, > >> i would like to panic() system and obtain a minidump. > >> > >> i have modified isa_nmi() to appropriately inspect bits and return > >> non-zero return code. i have turned off machdep.kdb_on_nmi knob (set > >> it to zero). i have confirmed that amd64 trap() is called with correct > >> T_NMI type. i've also confirmed that panic() is called from amd64's > >> trap(). > >> > >> the issue i have is that system is rebooting too early. basically, it > >> looks like minidump is started, but, for whatever reason, other cpus > >> are not completely stopped (or may be they are panic()ing again) and > >> system just reboots without having complete the minidump. > >> > >> the issue is not present when machdep.kdb_on_nmi is set to 1. in this > >> case, system drops into ddb prompt and 'call doadump' works as > >> expected. for various reasons i can not use ddb, and, would like to > >> have system save nmi triggered minidump completely unattended. > >> > >> can someone please give me a clue as to what i should be looking into > >> to make this work? > > > > could it be that more than one CPUs get the NMI at the same time? > > i guess, its possible. is there an easy way to check for that? > > > IF yes, then the current code wouldn't handle that well - each of the NMI-ed > > CPUs will try to stop all others with another NMI and it will wait until each of > > those CPUs sets an acknowledgement bit in its NMI handler. This scheme works > > fine if there's only one CPU that wants to become the master, but results in a > > deadlock otherwise. > > that makes sense. i don't observe deadlock, but, simple reboot. I believe I posted patches to serialize ddb entrance or panics due to nmi. I do not have references handy, you could search lists.
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