Date: Sat, 7 Dec 2019 01:16:13 +0100 From: Hans Petter Selasky <hps@selasky.org> To: Alexander Motin <mav@FreeBSD.org>, sgk@troutmask.apl.washington.edu Cc: Warner Losh <imp@bsdimp.com>, FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: CAM breaks USB [was Re: USB causing boot to hang] Message-ID: <3e5ead69-b933-70a4-a183-67552d8932fb@selasky.org> In-Reply-To: <3df3ff25-9f62-6f0f-7823-e846a43725eb@FreeBSD.org> References: <20191206202316.GA1053@troutmask.apl.washington.edu> <20191206223144.GA3224@troutmask.apl.washington.edu> <CANCZdfrvTmb0xfQ_A6vLdzgNziSHSsD5TBiC1DCnriTaWcr-nw@mail.gmail.com> <20191206225231.GA949@troutmask.apl.washington.edu> <dd35656e-2cbb-f889-64dc-89d15c471e37@FreeBSD.org> <20191206234105.GA1027@troutmask.apl.washington.edu> <3df3ff25-9f62-6f0f-7823-e846a43725eb@FreeBSD.org>
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On 2019-12-07 01:09, Alexander Motin wrote: > On 06.12.2019 18:41, Steve Kargl wrote: >> On Fri, Dec 06, 2019 at 06:15:32PM -0500, Alexander Motin wrote: >>> On 06.12.2019 17:52, Steve Kargl wrote: >>>> On Fri, Dec 06, 2019 at 03:33:09PM -0700, Warner Losh wrote: >>>>> On Fri, Dec 6, 2019 at 3:31 PM Steve Kargl <sgk@troutmask.apl.washington.edu> >>>>> wrote: >>>>>> The problem seems to be caused 355010. This is a commit to >>>>>> fix CAM, which seems to break USB. >>>>>> >>>>> Yes. mav@ made this change... >>>>> >>>> src/UPDATING seems to be missing an entry about CAM breaking USB. >>> >>> And also that moon is made of cheese. :-\ >> >> Not sure what you mean. > > I mean that if we are going to write there random fairy-tales, then I > prefer my moon. > > If serious, then my change did not change semantics of any existing > tunables, only the way some of them are implemented, so there was > nothing to write in UPDATING. > >> You made a change, and the commit log >> even notes that there could be an issue. Yet, you want a user >> to waste half a day finding the root cause of the problem. > > I am sorry that you wasted your time, but quick and ungrounded blames is > the last thing I want to read on Friday evening after the long day. > >>>> The commit message for 355010 states: >>>> >>>> Devices appearing on USB bus later may still require setting >>>> kern.cam.boot_delay, but hopefully those are minority. >>>> >>>> There is no statement about "where" kern.cam.boot_delay should be set. >>>> There is no statement about "what" value(s) kern.cam.boot_delay should be. >>> >>> If you never needed it before, you still don't need it. >> >> Prior to 355010 the system just boots up. After 355010 >> the system hangs. Will kern.cam.boot_delay paper over >> whatever (latent?) bug you've exposed? > > My change affected the timing of system boot process, allowing system to > continue booting some further, not waiting for CAM to scan its buses and > disks. If the problem is reproducible even without USB storage, then > CAM probably does not wait for it, so it is not the problem I first > thought about. > >>> If system hangs even without any USB disk attached, then I don't see a >>> relation between CAM and USB here. My change could affect some timings >>> of the boot process, but without closer debugging it is hard to guess >>> something. To be sure whether USB is related I would try to disable all >>> USB controllers either in BIOS or with set of loader tunables like >>> hint.ehci.0.disabled=1 , hint.ohci.0.disabled=1 , >>> hint.xhci.0.disabled=1, ... >> >> Yep. Completely disabling USB allows the system to boot. I don't >> see how this would be unexpected as umass using cam. > > umass uses CAM, but you've told the problem happens even without umass, > that is why I told that I don't see any relation. Does disabling of > _all_ USB fixes the problem? Have you tried to narrow it down to > specific controller or device? > > Is there anything special in your system? Are you running GENERIC > kernel? If not, then what do you have changed? > > If your kernel includes VERBOSE_SYSINIT as GENERIC does, I would try to > set debug.verbose_sysinit=1 and see how far the boot process goes and at > which stage it may is hanging (if we guess that hang is related to the > stage and not asynchronous). > Hi, There is an option you can compile into the kernel which will allow the keyboard to enter the debugger. options ALT_BREAK_TO_DEBUGGER Sounds to me like either a leaked refcount or that one thread is spinning blocking execution of other threads. --HPS
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