Date: Wed, 1 Dec 2021 14:35:50 -0700 From: Alan Somers <asomers@freebsd.org> To: Warner Losh <imp@bsdimp.com> Cc: FreeBSD <freebsd-stable@freebsd.org> Subject: Re: ZFS deadlocks triggered by HDD timeouts Message-ID: <CAOtMX2hGODt0hiwzOrThOQ=Sm1V%2B9my27pWwzp1L-hz3XWAVeQ@mail.gmail.com> In-Reply-To: <CANCZdfr_s_10zePSWoaVyi7ExcG9yqK=v5oDjLnVCVZ05hDJAw@mail.gmail.com> References: <CAOtMX2hMu7qXqHt5rhi9CBNDRERpWshcF%2BR9N_VQOrYvYFERQg@mail.gmail.com> <CANCZdfo7W-eFoQ6X4y0rY=k5in6T7Ledjhes39ToO9ZXLXyVbw@mail.gmail.com> <CAOtMX2jmppMTwnK_g4OiWSnGu=Vwxm1FMa-_izdNPTYaJPyiDA@mail.gmail.com> <CANCZdfqfcbObUUonrEdNViJ-5xvU%2BFeYT%2BapHwmTpiHmfBVaXg@mail.gmail.com> <CAOtMX2gnEgGn-h16UJHhrS79ypH357=r2R0DaYAa1J-TOGAKCQ@mail.gmail.com> <CANCZdfr_s_10zePSWoaVyi7ExcG9yqK=v5oDjLnVCVZ05hDJAw@mail.gmail.com>
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On Wed, Dec 1, 2021 at 1:56 PM Warner Losh <imp@bsdimp.com> wrote: > > > > On Wed, Dec 1, 2021 at 1:47 PM Alan Somers <asomers@freebsd.org> wrote: >> >> On Wed, Dec 1, 2021 at 1:37 PM Warner Losh <imp@bsdimp.com> wrote: >> > >> > >> > >> > On Wed, Dec 1, 2021 at 1:28 PM Alan Somers <asomers@freebsd.org> wrote: >> >> >> >> On Wed, Dec 1, 2021 at 11:25 AM Warner Losh <imp@bsdimp.com> wrote: >> >> > >> >> > >> >> > >> >> > On Wed, Dec 1, 2021, 11:16 AM Alan Somers <asomers@freebsd.org> wrote: >> >> >> >> >> >> On a stable/13 build from 16-Sep-2021 I see frequent ZFS deadlocks >> >> >> triggered by HDD timeouts. The timeouts are probably caused by >> >> >> genuine hardware faults, but they didn't lead to deadlocks in >> >> >> 12.2-RELEASE or 13.0-RELEASE. Unfortunately I don't have much >> >> >> additional information. ZFS's stack traces aren't very informative, >> >> >> and dmesg doesn't show anything besides the usual information about >> >> >> the disk timeout. I don't see anything obviously related in the >> >> >> commit history for that time range, either. >> >> >> >> >> >> Has anybody else observed this phenomenon? Or does anybody have a >> >> >> good way to deliberately inject timeouts? CAM makes it easy enough to >> >> >> inject an error, but not a timeout. If it did, then I could bisect >> >> >> the problem. As it is I can only reproduce it on production servers. >> >> > >> >> > >> >> > What SIM? Timeouts are tricky because they have many sources, some of which are nonlocal... >> >> > >> >> > Warner >> >> >> >> mpr(4) >> > >> > >> > Is this just a single drive that's acting up, or is the controller initialized as part of the error recovery? >> >> I'm not doing anything fancy with mprutil or sas3flash, if that's what >> you're asking. > > > No. I'm asking if you've enabled debugging on the recovery messages and see that we enter any kind of > controller reset when the timeouts occur. No. My CAM setup is the default except that I enabled CAM_IO_STATS and changed the following two sysctls: kern.cam.da.retry_count=2 kern.cam.da.default_timeout=10 > >> >> > If a single drive, >> > are there multiple timeouts that happen at the same time such that we timeout a request while we're waiting for >> > the abort command we send to the firmware to be acknowledged? >> >> I don't know. > > > OK. > >> >> > Would you be able to run a kgdb script to see >> > if you're hitting a situation that I fixed in mpr that would cause I/O to never complete in this rather odd circumstance? >> > If you can, and if it is, then there's a change I can MFC :). >> >> Possibly. When would I run this kgdb script? Before ZFS locks up, >> after, or while the problematic timeout happens? > > > After the timeouts. I've been doing 'kgdb' followed by 'source mpr-hang.gdb' to run this. > > What you are looking for is anything with a qfrozen_cnt > 0.. The script is imperfect and racy > with normal operations (but not in a bad way), so you may need to run it a couple of times > to get consistent data. On my systems, there'd be one or two devices with a frozen count > 1 > and no I/O happened on those drives and processes hung. That might not be any different than > a deadlock :) > > Warner > > P.S. here's the mpr-hang.gdb script. Not sure if I can make an attachment survive the mailing lists :) Thanks, I'll try that. If this is the problem, do you have any idea why it wouldn't happen on 12.2-RELEASE (I haven't seen it on 13.0-RELEASE, but maybe I just don't have enough runtime on that version). > > Warner
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