Date: Thu, 14 Oct 2010 15:23:34 +0100 From: "Robert N. M. Watson" <rwatson@freebsd.org> To: Attilio Rao <attilio@freebsd.org> Cc: FreeBSD Current <current@freebsd.org>, freebsd-net@freebsd.org, Sergey Kandaurov <pluknet@freebsd.org>, Jack F Vogel <jfv@freebsd.org>, Ryan Stone <rstone@sandvine.com>, Ryan Stone <rysto32@gmail.com>, Ed Maste <emaste@sandvine.com> Subject: Re: [PATCH] Netdump for review and testing -- preliminary version Message-ID: <15387E38-1E6C-4347-BEA1-61AEE31B5544@freebsd.org> In-Reply-To: <AANLkTimLnRsa4v=A3Ui-1hKiVc5YLwkBND4NOmT4t%2BtB@mail.gmail.com> References: <AANLkTikA5OUYD1A9pqCqVEZ5qk%2BVECq8x-fnRXnpp0KE@mail.gmail.com> <AANLkTikau6omhWrXVM13zonFEPCxXM%2B8EqJauovDu0OU@mail.gmail.com> <alpine.BSF.2.00.1010090121310.1232@fledge.watson.org> <AANLkTimisSojDg2z_f1_v71evfooVdPQ44eu2Thhrf3O@mail.gmail.com> <C73FFD46-80B0-44F0-9A19-2B047C285134@freebsd.org> <AANLkTimLnRsa4v=A3Ui-1hKiVc5YLwkBND4NOmT4t%2BtB@mail.gmail.com>
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On 14 Oct 2010, at 15:10, Attilio Rao wrote: >> My concern is less about occasional lost dumps that destabilising the = dumping process: calls into the memory allocator can currently trigger a = lot of interesting behaviours, such as further calls back into the VM = system, which can then trigger calls into other subsystems. What I'm = suggesting is that if we want the mbuf allocator to be useful in this = context, we need to teach it about things not to do in the dumping / = crash / ... context, which probably means helping uma out a bit in that = regard. And a watchdog to make sure the dump is making progress. >=20 > I think that this would be way too complicated just to cope with panic > within the VM/UMA (not sure what other subsystems you are referring > to, wrt supposed to call). Besides, if we have a panic in the VM I'm > sure that normal dumps could also be affected. > When dealing with netdump, I'm not trying to fix all the bugs related > to our dumping infrastructure because, as long as we already > discussed, we know there are quite a few of them, but trying at least > to follow the same fragile-ness than what we have today. > And again, while I think the "watchdog" idea is good, I think it still > applies to normal dumps too, it is not specific to netdump. No, what I'm saying is: UMA needs to not call its drain handlers, and = ideally not call into VM to fill slabs, from the dumping context. That's = easy to implement and will cause the dump to fail rather than causing = the system to hang. Robert=
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