sunny.s.zhang posted on Tue, 18 Sep 2018 08:28:14 +0800 as excerpted: > My OS(4.1.12) panic in kmem_cache_alloc, which is called by > btrfs_get_or_create_delayed_node. > > I found that the freelist of the slub is wrong.
[Not a dev, just a btrfs list regular and user, myself. But here's a general btrfs list recommendations reply...] You appear to mean kernel 4.1.12 -- confirmed by the version reported in the posted dump: 4.1.12-112.14.13.el6uek.x86_64 OK, so from the perspective of this forward-development-focused list, kernel 4.1 is pretty ancient history, but you do have a number of options. First let's consider the general situation. Most people choose an enterprise distro for supported stability, and that's certainly a valid thing to want. However, btrfs, while now reaching early maturity for the basics (single device in single or dup mode, and multi-device in single/ raid0/1/10 modes, note that raid56 mode is newer and less mature), remains under quite heavy development, and keeping reasonably current is recommended for that reason. So you you chose an enterprise distro presumably to lock in supported stability for several years, but you chose a filesystem, btrfs, that's still under heavy development, with reasonably current kernels and userspace recommended as tending to have the known bugs fixed. There's a bit of a conflict there, and the /general/ recommendation would thus be to consider whether one or the other of those choices are inappropriate for your use-case, because it's really quite likely that if you really want the stability of an enterprise distro and kernel, that btrfs isn't as stable a filesystem as you're likely to want to match with it. Alternatively, if you want something newer to match the still under heavy development btrfs, you very likely want a distro that's not focused on years-old stability just for the sake of it. One or the other is likely to be a poor match for your needs, and choosing something else that's a better match is likely to be a much better experience for you. But perhaps you do have reason to want to run the newer and not quite to traditional enterprise-distro level stability btrfs, on an otherwise older and very stable enterprise distro. That's fine, provided you know what you're getting yourself into, and are prepared to deal with it. In that case, for best support from the list, we'd recommend running one of the latest two kernels in either the current or mainline LTS tracks. For current track, With 4.18 being the latest kernel, that'd be 4.18 or 4.17, as available on kernel.org (tho 4.17 is already EOL, no further releases, at 4.17.19). For mainline-LTS track, 4.14 and 4.9 are the latest two LTS series kernels, tho IIRC 4.19 is scheduled to be this year's LTS (or was it 4.18 and it's just not out of normal stable range yet so not yet marked LTS?), so it'll be coming up soon and 4.9 will then be dropping to third LTS series and thus out of our best recommended range. 4.4 was the previous LTS and while still in LTS support, is outside the two newest LTS series that this list recommends. And of course 4.1 is older than 4.4, so as I said, in btrfs development terms, it's quite ancient indeed... quite out of practical support range here, tho of course we'll still try, but in many cases the first question when any problem's reported is going to be whether it's reproducible on something closer to current. But... you ARE on an enterprise kernel, likely on an enterprise distro, and very possibly actually paying /them/ for support. So you're not without options if you prefer to stay with your supported enterprise kernel. If you're paying them for support, you might as well use it, and of course of the very many fixes since 4.1, they know what they've backported and what they haven't, so they're far better placed to provide that support in any case. Or, given what you posted, you appear to be reasonably able to do at least limited kernel-dev-level analysis yourself. Given that, you're already reasonably well placed to simply decide to stick with what you have and take the support you can get, diving into things yourself if necessary. So those are your kernel options. What about userspace btrfs-progs? Generally speaking, while the filesystem's running, it's the kernel code doing most of the work. If you have old userspace, it simply means you can't take advantage of some of the newer features as the old userspace doesn't know how to call for them. But the situation changes as soon as you have problems and can't mount, because it's userspace code that runs to try to fix that sort of problem, or failing that, it's userspace code that btrfs restore runs to try to grab what files can be grabbed off of the unmountable filesystem. So for routine operation, it's no big deal if userspace is a bit old, at least as long as it's new enough to have all the newer command formats, etc, that you need, and for comparing against others when posted. But once things go bad on you, you really want the newest btrfs-progs in ordered to give you the best chance at either fixing things, or worst- case, at least retrieving the files off the dead filesystem. So using the older distro btrfs-progs for routine running should be fine, but unless your backups are complete and frequent enough that if something goes wrong it's easiest to simply blow the bad version away with a fresh mkfs and start over, you'll probably want at least a reasonably current btrfs-progs on your rescue media at least. Since the userspace version numbers are synced to the kernel cycle, a good rule of thumb is keep your btrfs-progs version to at least that of the oldest recommended LTS kernel version, as well, so you'd want at least btrfs-progs 4.9 on your rescue media, for now, and 4.14, coming up, since when the new kernel goes LTS that'll displace 4.9 and 4.14 will then be the second-back LTS. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman
