On Sun, Nov 14, 2010 at 9:59 PM, Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > On Mon, Nov 08 2010 at 12:59pm -0500, > Chris Mason <chris.mason@xxxxxxxxxx> wrote: > >> Excerpts from Mike Snitzer's message of 2010-11-08 09:58:09 -0500: >> > On Sun, Nov 07 2010 at 6:05pm -0500, >> > Andi Kleen <andi@xxxxxxxxxxxxxx> wrote: >> > >> > > On Sun, Nov 07, 2010 at 10:39:23PM +0100, Milan Broz wrote: >> > > > On 11/07/2010 08:45 PM, Andi Kleen wrote: >> > > > >> I read about barrier-problems and data getting to the partition when >> > > > >> using dm-crypt and several layers so I don't know if that could be >> > > > >> related >> > > > > >> > > > > Barriers seem to be totally broken on dm-crypt currently. >> > > > >> > > > Can you explain it? >> > > >> > > e.g. the btrfs mailing list is full of corruption reports >> > > on dm-crypt and most of the symptoms point to broken barriers. >> > >> > [cc'ing linux-btrfs, hopefully in the future dm-devel will get cc'd when >> > concerns about DM come up on linux-btrfs (or other lists)] >> > >> > I spoke with Josef Bacik and these corruption reports are apparently >> > against older kernels (e.g. <= 2.6.33). I say <= 2.6.33 because: >> >> We've consistently seen reports about corruptions on power hits with >> dm-crypt. The logs didn't have any messages about barriers failing, but >> the corruptions were still there. The most likely cause is that >> barriers just aren't getting through somehow. > > Can't blame anyone for assuming as much (although it does create FUD) > but in practice (testing dm-crypt with ext4 using your barrier-test > script) I have not been able to see any evidence that dm-crypt's barrier > support is ineffective. > > Could be that the barrier-test script isn't able to reproduce the unique > failure case that btrfs does (on power failure)? > >> > > > Barriers/flush change should work, if it is broken, it is not only dm-crypt. >> > > > (dm-crypt simply relies on dm-core implementation, when barrier/flush >> > > > request come to dmcrypt, all previous IO must be already finished). >> > > >> > > Possibly, at least it doesn't seem to work. >> > >> > Can you please be more specific? What test(s)? What kernel(s)? >> > >> > Any pointers to previous (and preferably: recent) reports would be >> > appreciated. > > I still think we need specific bug reports that detail workloads and if > possible reproducers. > >> > The DM barrier code has seen considerable change recently (via flush+fua >> > changes in 2.6.37). Those changes have been tested quite a bit >> > (including ext4 consistency after a crash). >> > >> > But even prior to those flush+fua changes DM's support for barriers >> > (Linux >= 2.6.31) was held to be robust. No known (at least no >> > reported) issues with DM's barrier support. >> >> I think it would be best to move forward with just hammering on the >> dm-crypt barriers: >> >> http://oss.oracle.com/~mason/barrier-test >> >> This script is the best I've found so far to reliably trigger >> corruptions with barriers off. I'd start with ext3 + barriers off just >> to prove it corrupts things, then move to ext3 + barriers on. > > I started with ext4 + barrier=0,journal_async_commit and could reliably > cause directory corruption (~75% of the time). I then switched to > barrier=1 and could not cause corruption. > > I then added dm-crypt and got the same results: with barrier=1 I could > not cause directory corruption. barrier=0 resulted in directory > corruption (again ~75% of the time), no corruption occurred with > barrier=1. > > Both 2.6.36 (original barrier code) and latest 2.6.37-rc1+ (new > flush+fua code) were tested. 6 iterations of barrier=0 and 10 > iterations of barrier=1. > > So my hope is we can now put this general dm-crypt barrier doubt to one > side and work together on identifying the cause of corruption when > dm-crypt is paired with btrfs. > > Thanks, > Mike > Hi Mike, I'm pretty sure that dm-crypt is rockstable :) My report wasn't meant to be / cause FUD sorry if it got picked up that way: with the vanilla dm-crypt implementation I saw *NO* corruption at all in the small testing amount of time I ran it however as soon as I applied the [PATCH] DM-CRYPT: Scale to multiple CPUs v3 and [PATCH] Fix double free and use generic private pointer in per-cpu patches, recompiled the kernel and rebooted into that new environment it seemingly caused corruptions right from the start (the mentioned corruption /etc/env.d/02opengl to be the most obvious candidate and probably even more) with those corruptions being anticipated over longer uptime and heavy use-patterns (such as re-compiling the whole system). I don't know if the new multi-cpu scaling patch for dm-crypt makes a change (since I can't test it right now due to a busy schedule) [PATCH v5] dm crypt: scale to multiple CPUs I however have a request: could you guys please take this patch through a "battery of heavy tests" until it's included in mainline ? so that you can spot any issues (races, BUGs, etc.) which might be inherent/triggered in current dm-crypt so that my reported corruptions might be prevented in the future ? Again: the vanilla kernel and dm-crypt are perfectly stable ! only with the dm-crypt scaling patch I could observe the data-corruption Thanks ! Matt -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
