Date: Thu, 7 Jan 2016 22:31:24 +0100 From: Hans Petter Selasky <hps@selasky.org> To: Mark Millard <markmi@dsl-only.net> Cc: freebsd-arm <freebsd-arm@freebsd.org>, Ian Lepore <ian@freebsd.org> Subject: Re: FYI: various 11.0-CURRENT -r293227 (and older) hangs on arm (rpi2): a description of sorts Message-ID: <568ED92C.9070602@selasky.org> In-Reply-To: <568ED810.8010309@selasky.org> References: <E0379BE9-308A-4219-A8AE-A5FFE828BA93@dsl-only.net> <1452183170.1215.4.camel@freebsd.org> <FB0D5486-AD27-44A7-86CA-68989AE08EC7@dsl-only.net> <1452196099.1215.12.camel@freebsd.org> <568EC4D8.7010106@selasky.org> <8B728C93-9C90-4821-A607-5D157F028812@dsl-only.net> <568ED810.8010309@selasky.org>
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On 01/07/16 22:26, Hans Petter Selasky wrote: > On 01/07/16 21:20, Mark Millard wrote: >> >> On 2016-Jan-7, at 12:04 PM, Hans Petter Selasky <hps at selasky.org> >> wrote: >>> >>> On 01/07/16 20:48, Ian Lepore wrote: >>>> If the filesystems and swap space are on a usb drive, then maybe it's >>>> the usb subsystem that's hanging. The wait states you showed for those >>>> processes are consistant with what I've seen when all buffers get >>>> backed up in a queue on one non-responsive or slow device. It may be >>>> that there's a way to get the system deadlocked when it's low on >>>> buffers and there is memory pressure causing the swap to be used (I >>>> generally run arms systems without any swap configured). >>>> >>>> Running gstat in another window while this is going on may give you >>>> some insight into the situation. Beyond that I don't know what to look >>>> at, especially since you generally can't launch any new tools once the >>>> system gets into this kind of state. >>>> >>>> -- Ian >>> >>> Hi, >>> >>> All USB transfers towards disk devices have timeouts, so if something >>> is hanging at USB level, you'll get a printout eventually. >> >> What sort of timescale after deadlock/live-lock is observed to >> apparently have started does one have to wait in order to conclude >> that the timeouts would have happened and so they do not apply to the >> deadlock/live-lock? >> >>> The USB kernel processes needed for doing I/O transfers are not >>> pinned to RAM. Can it happen if a USB process is swapped to disk, >>> that the system cannot wakeup a swapped out process to get more swap? >>> >>> --HPS >> > > Hi, > >> Wow. Could I use ddb to somehow check on the "USB kernel processes" >> swap status when the overall context is deadlocked/live-locked? > > Are you able to run something like: > > ps auxwwH | grep usb > > > If yes, how? Otherwise something in top or some such display that I'd > left running over the serial console would have to present useful > information on the subject. Is there anything that would? > Are you able to SSH into the box or ping it? --HPS
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