Date: Wed, 22 Nov 2017 11:26:10 -0500 From: Youzhong Yang <youzhong@gmail.com> To: Andriy Gapon <avg@freebsd.org> Cc: Shiva Bhanujan <Shiva.Bhanujan@quorum.com>, "cem@freebsd.org" <cem@freebsd.org>, "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org> Subject: Re: zio_done panic in 10.3 Message-ID: <CADpNCvawxn1wkaEjp_9TFTfMWtaLD20ei--gNTGfsTdA9ELqUg@mail.gmail.com> In-Reply-To: <78d712d9-dda3-0411-262e-bb64f9ab46eb@FreeBSD.org> References: <3A5A10BE32AC9E45B4A22F89FC90EC0701C367D3D1@QLEXC01.Quorum.local> <5021a016-9193-b626-78cf-54ffa3929e22@FreeBSD.org> <3A5A10BE32AC9E45B4A22F89FC90EC0701C367D562@QLEXC01.Quorum.local> <CAG6CVpVT=4iid4xi0yw3AJe4kbBNEGj6zVCKfozq_-8CgGYfag@mail.gmail.com> <3A5A10BE32AC9E45B4A22F89FC90EC0701C367D636@QLEXC01.Quorum.local> <41e2465d-e1b5-33ce-57b5-49bea6087d9a@FreeBSD.org> <CADpNCvbpSTFjSHHVGV_=-LK27XLSzfZi_gzSa0v-Z=h_msOQuw@mail.gmail.com> <78d712d9-dda3-0411-262e-bb64f9ab46eb@FreeBSD.org>
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Thanks Andriy. Two bug reports filed: https://www.illumos.org/issues/8857 https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=223803 On Wed, Nov 22, 2017 at 10:22 AM, Andriy Gapon <avg@freebsd.org> wrote: > On 22/11/2017 16:40, Youzhong Yang wrote: > > Hi Andriy, > > > > This is nice! I am 100% sure it's exactly the same issue I experienced > and then > > reported to illumos mailing list. In all the crash dumps zio->io_done = > > l2arc_read_done, so I thought the crash must be related to L2ARC. Once I > set > > secondarycache=metadata, the frequency of crash went from one per 2 days > down to > > one per week. I've been puzzled by what could have caused a zio being > destroyed > > while there's still child zio. Your explanation definitely makes sense! > > Oh, I now recall seeing your report: > https://illumos.topicbox.com/groups/zfs/Tccd8b4463865899e > I remember that it raised my interest, but then I forgot about it and > didn't > correlate it with the latest reports. > > > By the way, is there a FreeBSD bug report or an illumos bug number > tracking this > > issue? I would be more than happy to create one if needed, and also test > your > > potential fix here in our environment. > > I am not aware of any existing bug report. > It would be great if you could open one [ or two :-) ] > If you open an illumos issue, please also add George Wilson as a watcher. > I think that George is also interested in fixing this issue and he knows > the > relevant code better than me. > > Thank you! > > > On Tue, Nov 21, 2017 at 3:46 PM, Andriy Gapon <avg@freebsd.org > > <mailto:avg@freebsd.org>> wrote: > > > > > > > > > > On 21/11/2017 21:30, Shiva Bhanujan wrote: > > > it did get compressed to 0.5G - still too big to send via email. > I did send some more debug information by running kgdb on the core file to > Andriy, and I'm waiting for any analysis that he might provide. > > > > Yes, kgdb-over-email turned out to be a far more efficient > compression :-) > > I already have an analysis based on the information provided by > Shiva and by > > another user who has the same problem and contacted me privately. > > I am discussing possible ways to fix the problem with George Wilson > who was very > > kind to double-check the analysis, complete it and suggest possible > fixes. > > > > A short version is that dbuf_prefetch and > dbuf_prefetch_indirect_done functions > > chain new zio-s under the same parent zio (a completion of one child > zio may > > create another child zio). They do it using arc_read which can > create either a > > logical zio in most cases or a vdev zio for a read from a cache > device (2arc). > > zio_done() has a check for the completion of a parent zio's children > but that > > check is not completely safe and can be broken by the pattern that > dbuf_prefetch > > can create. So, under some specific circumstances the parent zio > may complete > > and get destroyed while there is a child zio. > > > > I believe this problem to be rather rare, but there could be > configurations and > > workloads where it's triggered more often. > > The problem does not happen if there are no cache devices. > > > > > From: Conrad Meyer [cem@freebsd.org <mailto:cem@freebsd.org>] > > > > > > Sent: Tuesday, November 21, 2017 9:04 AM > > > > > > To: Shiva Bhanujan > > > > > > Cc: Andriy Gapon; freebsd-fs@freebsd.org <mailto: > freebsd-fs@freebsd.org> > > > > > > Subject: Re: zio_done panic in 10.3 > > > > > > > > > > > > > > > > > > > > > > > > Have you tried compressing it with e.g. xz or zstd? > > > > > > -- > > Andriy Gapon > > _______________________________________________ > > freebsd-fs@freebsd.org <mailto:freebsd-fs@freebsd.org> mailing list > > https://lists.freebsd.org/mailman/listinfo/freebsd-fs > > <https://lists.freebsd.org/mailman/listinfo/freebsd-fs>; > > To unsubscribe, send any mail to "freebsd-fs-unsubscribe@freebsd.org > > <mailto:freebsd-fs-unsubscribe@freebsd.org>" > > > > > > > -- > Andriy Gapon >
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