On Mon, Sep 16, 2019 at 02:45:56PM +0300, Janne Karhunen wrote: > On Sun, Sep 15, 2019 at 11:24 PM Eric Biggers <ebiggers@xxxxxxxxxx> wrote: > > > > > This still doesn't make it crash-safe. So why is it okay? > > > > > > If Android is the load, this makes it crash safe 99% of the time and > > > that is considerably better than 0% of the time. > > > > > > > Who will use it if it isn't 100% safe? > > I suppose anyone using mutable data with IMA appraise should, unless > they have a redundant power supply and a kernel that never crashes. In > a way this is like asking if the ima-appraise should be there for > mutable data at all. All this is doing is that it improves the crash > recovery reliability without taking anything away. Okay, so why would anyone use mutable data with IMA appraise if it corrupts your files by design, both with and without this patchset? > > Anyway, I think I'm getting along with my understanding of the page > writeback slowly and the journal support will eventually be there at > least as an add-on patch for those that want to use it and really need > the last 0.n% reliability. Note that even without that patch you can > build ima-appraise based systems that are 99.999% reliable just by On what storage devices, workloads, and filesystems is this number for? > having the patch we're discussing here. Without it you would be orders > of magnitude worse off. All we are doing is that we give it a fairly > good chance to recover instead of giving up without even trying. > > That said, I'm not sure the 100% crash recovery is ever guaranteed in > any Linux system. We just have to do what we can, no? > Filesystems implement consistency mechanisms, e.g. journalling or copy-on-write, to recover from crashes by design. This patchset doesn't implement or use any such mechanism, so it's not crash-safe. It's not clear that it's even a step in the right direction, as no patches have been proposed for a correct solution so we can see what it actually involves. - Eric
