Date: Fri, 3 Dec 2021 17:25:48 -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: <CAOtMX2gi1ir7QauGu3H%2BdJZdPcj91SbypRQ53npwP1Xxf6Z_DA@mail.gmail.com> In-Reply-To: <CANCZdfoVQvkM62WuUB4btjg14Vau0rsoaauEGPP_Qitqo8U_Fw@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> <CAOtMX2hGODt0hiwzOrThOQ=Sm1V%2B9my27pWwzp1L-hz3XWAVeQ@mail.gmail.com> <CANCZdfrruAVxMvuN60b2a_70zD0Q5jNh31BKqVt%2BxX_eo4=nig@mail.gmail.com> <CAOtMX2j5kGy3Ef9dmJbhMhi4sYJ%2BSfYmBk6O4%2BVH-ZrTDdq0uw@mail.gmail.com> <CANCZdfqy=hLkBYLK8rJy2JOGvM0CwqMVpFYstchMp2JW49J2GQ@mail.gmail.com> <CAOtMX2js0dtvpZ9SJM6o3VfAr9-swWBt9725V2pJkZZrxUMh3Q@mail.gmail.com> <CANCZdfoVQvkM62WuUB4btjg14Vau0rsoaauEGPP_Qitqo8U_Fw@mail.gmail.com>
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On Fri, Dec 3, 2021 at 5:19 PM Warner Losh <imp@bsdimp.com> wrote: > > Hey Alan, > > On Fri, Dec 3, 2021 at 8:38 AM Alan Somers <asomers@freebsd.org> wrote: >> >> On Wed, Dec 1, 2021 at 3:48 PM Warner Losh <imp@bsdimp.com> wrote: >> > >> > >> > >> > On Wed, Dec 1, 2021, 3:36 PM Alan Somers <asomers@freebsd.org> wrote: >> >> >> >> On Wed, Dec 1, 2021 at 2:46 PM Warner Losh <imp@bsdimp.com> wrote: >> >> > >> >> > >> >> > >> >> > >> >> > On Wed, Dec 1, 2021, 2:36 PM Alan Somers <asomers@freebsd.org> wrote: >> >> >> >> >> >> 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). >> >> > >> >> > >> >> > 9781c28c6d63 was merged to stable/13 as a996b55ab34c on Sept 2nd. I fixed a bug >> >> > with that version in current as a8837c77efd0, but haven't merged it. I kinda expect that >> >> > this might be the cause of the problem. But in Netflix's fleet we've seen this maybe a >> >> > couple of times a week over many thousands of machines, so I've been a little cautious >> >> > in merging it to make sure that it's really fixed. So far, the jury is out. >> >> > >> >> > Warner >> >> >> >> Well, I'm experiencing this error much more frequently than you then. >> >> I've seen it on about 10% of similarly-configured servers and they've >> >> only been running that release for 1 week. >> > >> > >> > You can run my script soon then to see if it's the same thing. >> > >> > Warner >> > >> >> -Alan >> >> That confirms it. I hit the deadlock again, and qfrozen_cnt was >> between 1 and 3 for four devices: two da devices (we use multipath) >> and their accompanying pass devices. So I should try merging >> a8837c77efd0 next? > > > Yes. I'd planned on merging it this weekend, but if you wanted a jump > on me, that's the next step. > > Warner It merged without conflict, and I'm testing it now. But without a way to inject timeouts I can't tell whether it's working. -Alan
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