Date: Sat, 22 Nov 2014 17:09:09 +0000 From: "Robert N. M. Watson" <rwatson@FreeBSD.org> To: Adrian Chadd <adrian@freebsd.org> Cc: Craig Rodrigues <rodrigc@freebsd.org>, FreeBSD Net <freebsd-net@freebsd.org>, "Bjoern A. Zeeb" <bz@freebsd.org>, Marko Zec <zec@fer.hr> Subject: Re: VIMAGE UDP memory leak fix Message-ID: <85C7A32E-121D-495F-93C7-9D2B2F134FF6@FreeBSD.org> In-Reply-To: <CAJ-VmokymFoLhCFQqqqa0NXKw4EVwkKQ8ZUjATOTR5EjRyvjKw@mail.gmail.com> References: <CAG=rPVehky00X4MuQQ-_Oe5ezWg52ZZrPASAh9GBy7baYv78CA@mail.gmail.com> <20141121002937.4f82daea@x23> <A4D676B3-6C50-47F7-8CFD-50B44FF4BE98@FreeBSD.org> <9300CB5F-6140-4C49-B026-EB69B0E8B37E@FreeBSD.org> <20141121120201.6c77ea5b@x23> <A4211137-9CE8-45A6-BA73-DCD767236C48@FreeBSD.org> <20141121162042.449b22dc@x23> <072B7B0F-4DE3-4D37-BC94-1DEA38CF3B12@FreeBSD.org> <CAJ-VmokymFoLhCFQqqqa0NXKw4EVwkKQ8ZUjATOTR5EjRyvjKw@mail.gmail.com>
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On 21 Nov 2014, at 17:40, Adrian Chadd <adrian@freebsd.org> wrote: >>> Skimming through a bunch of hosts with moderately loaded hosts with >>> reasonably high uptime I couldn't find one where = net.inet.tcp.timer_race >>> was not zero. A ny suggestions how to best reproduce the race(s) in >>> tcp_timer.c? >>=20 >> They would likely occur only on very highly loaded hosts, as they = require race conditions to arise between TCP timers and TCP close. I = think I did manage to reproduce it at one stage, and left the counter in = to see if we could spot it in production, and I have had (multiple) = reports of it in deployed systems. I'm not sure it's worth trying to = reproduce them, given that knowledge -- we should simply fix them. >=20 > Wasn't this just fixed by Julien @ Verisign? I don't believe so, although it's the kind of thing Julien is very good = at fixing! The issue here is that we can't call callout_drain() from contexts where = we finalise TCP connection close and attempt to free the inpcb. The = 'easy' fix is to create a taskqueue thread to do the callout_drain() in = the event that we discover that callout_stop() isn't able to guarantee = that pending callouts are neither in execution nor scheduled. We'd then = defer the very tail of TCP teardown to that asynchronous context rather = than trying to do it to completion in the current (and rather more = sensitive) one. This would happen only very in frequently so have little = overhead in practice, although one would want to carefully look at the = sync behaviour to make sure it wasn't frequently enough that a backlog = might build up. > As for the vimage stability side of things - I'd really like to see > some VIMAGE torture tests written. Stuff like "do a high rate TCP > connection test whilst creating and destroying VIMAGEs." ... and even for non-VIMAGE. :-) Robert
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