Date: Fri, 3 Dec 2021 17:28:03 -0700 From: Warner Losh <imp@bsdimp.com> To: Alan Somers <asomers@freebsd.org> Cc: FreeBSD <freebsd-stable@freebsd.org> Subject: Re: ZFS deadlocks triggered by HDD timeouts Message-ID: <CANCZdfr7TA7H1pb3CTe5P0qkA=uXCNFsSD7a1docWn%2B8%2BN=ksg@mail.gmail.com> In-Reply-To: <CAOtMX2gi1ir7QauGu3H%2BdJZdPcj91SbypRQ53npwP1Xxf6Z_DA@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> <CAOtMX2gi1ir7QauGu3H%2BdJZdPcj91SbypRQ53npwP1Xxf6Z_DA@mail.gmail.com>
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--0000000000006fef3905d2471928 Content-Type: text/plain; charset="UTF-8" Hey Alan, On Fri, Dec 3, 2021 at 5:26 PM Alan Somers <asomers@freebsd.org> wrote: > 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. > You can enable, at runtime, the 'recovery' messages from the mpr driver. >From those you'll know if you are hitting the timeout when timeout active case. dev.mpr.0.debug_level=info,fault,recovery is what I think I use. Warner --0000000000006fef3905d2471928--
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