Date: Fri, 21 Nov 2014 15:32:53 +0000 From: "Robert N. M. Watson" <rwatson@FreeBSD.org> To: Marko Zec <zec@fer.hr> Cc: Craig Rodrigues <rodrigc@freebsd.org>, FreeBSD Net <freebsd-net@freebsd.org>, "Bjoern A. Zeeb" <bz@FreeBSD.org> Subject: Re: VIMAGE UDP memory leak fix Message-ID: <072B7B0F-4DE3-4D37-BC94-1DEA38CF3B12@FreeBSD.org> In-Reply-To: <20141121162042.449b22dc@x23> 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>
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On 21 Nov 2014, at 15:20, Marko Zec <zec@fer.hr> wrote: >> Bjoern and I chatted for the last twenty or so minutes about the >> code, and believe that as things stand, it is *not* safe to turn off >> UMA_ZONE_NOFREE for TCP due to a teardown race in TCP that has been >> known about and discussed for several years, but is some work to >> resolve and that we've not yet found time to do so. The XXXRW's in >> tcp_timer.c are related to this. We're pondering ways to fix it but >> think this is not something that can be rushed. >=20 > OK fair enough - thanks a lot for looking into this! >=20 > 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? 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. Robert=
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