On Saturday 03 December 2016 13:42:42 Chris Murphy wrote: > On Sat, Dec 3, 2016 at 11:40 AM, Marc Joliet <mar...@gmx.de> wrote: > > Hello all, > > > > I'm having some trouble with btrfs on a laptop, possibly due to qgroups. > > Specifically, some file system activities (e.g., snapshot creation, > > baloo_file_extractor from KDE Plasma) cause the system to hang for up to > > about 40 minutes, maybe more. > > Do you get any blocked tasks kernel messages? If so, issue sysrq+w > during the hang, and then check the system log (dmesg may not contain > everything if the command fills the message buffer). If it's a hang > without any kernel messages, then issue sysrq+t. > > https://www.kernel.org/doc/Documentation/sysrq.txt
As it's a rescue shell, I have only the one shell AFAIK, and it's occupied by mount. So I can't tell if there are dmesg entries, however, when this happens during a normal running system, I never saw any dmesg entries. Anyway, I ran both. The output of sysrq+w mentions two tasks: "btrfs-transaction" with btrfs_scrub_pause+0xbe/0xd0 as the top-most entry in the call trace, and "mount" with its top-most entry at schedule+0x33/0x90 (it looks like it's still in the "early" processing, since there's also "btrfs_parse_early_options+0190/0x190" in the call trace). The output of sysrq+t is too big to capture all of it (i.e., I can't scroll back to the beginning), but just looking at the task names that I *can* see, there are: btrfs-fixup, various btrfs-endio*, btrfs-rmw, btrfs-freespace, btrfs-delayed-m (cut off), btrfs-readahead, btrfs-qgroup-re (cut off), btrfs- extent-re (cut off), btrfs-cleaner, and btrfs-transaction. Oh, and a bunch of kworkers. Should I take photos? That'll be annoying to do with all the scrolling, but I can do that if need be. > > After I next turned on the laptop, the balance resumed, causing bootup to > > fail, after which I remembered about the skip_balance mount option, which > > I > > tried in a rescue shell from an initramfs. > > The file system is the root filesystem? If so, skip_balance may not be > happening soon enough. Use kernel parameter rootflags=skip_balance > which will apply this mount option at the very first moment the file > system is mounted during boot. Yes, it's the root file system (there's that plus a swap partition). I believe I tried rootflags, but I think it also failed, which is why I'm using a rescue shell now. I can try it again, though, if anybody thinks that there's no point in waiting, especially if btrfs_scrub_pause in the btrfs- transaction call trace is significant. > > Since I couldn't use skip_balance, and logically can't destroy qgroups on > > a > > read-only file system, I decided to wait for a regular mount to finish. > > That has been running since Tuesday, and I am slowly growing impatient. > Haha, no kidding! I think that's very patient. Heh :) . I've still got my main desktop (as ancient as it may be), so I'm content with waiting for now, but I don't want to wait forever, especially if there might not even be a point. > > Thus I arrive at my question(s): is there anything else I can try, short > > of > > reformatting and restoring from backup? Can I use btrfs-check here, or > > any > > other tool? Or...? > > Yes, btrfs-progs 4.8.5 has the latest qgroup checks, so if there's > something wrong it should find it and if not that's a bug of its own. The initramfs has 4.8.4, but it looks like 4.8.5 was "only" an urgent bug fix, with no changes to qgroups handling, so I can use that, too. Can it repair qgroups problems, too? > > Also, should I be able to avoid reformatting: how do I properly disable > > quota support? > > 'btrfs quota disable' is the only command that applies to this and it > requires rw mount; there's no 'noquota' mount option. OK, thanks. So what should I try next? I'm sick at home, so I can spend more time on this than usual. -- Marc Joliet -- "People who think they know everything really annoy those of us who know we don't" - Bjarne Stroustrup
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