On Tue, Sep 29, 2020 at 05:15:38AM +0000, Nick Terrell wrote: > > > > On Sep 28, 2020, at 11:02 AM, Nick Terrell <terrelln@xxxxxx> wrote: > > > > > > > >> On Sep 28, 2020, at 1:55 AM, Feng Tang <feng.tang@xxxxxxxxx> wrote: > >> > >> Hi Nick, > >> > >> 0day has found some kernel decomprssion failure case since 5.9-rc1 (X86_32 > >> build), and it could be related with ZSTD code, though initially we bisected > >> to some other commits. > >> > >> The error messages are: > >> Decompressing Linux... > >> > >> ZSTD-compressed data is corrupt > >> > >> This could be reproduced by compiling the kernel with attached config, > >> and use QEMU to boot it. > >> > >> We suspect it could be related with the kernel size, as we only see > >> it on big kernel, and some more info are: > >> > >> * If we remove a lot of kernel config to build a much smaller kernel, > >> it will boot fine > >> > >> * If we change the zstd algorithm from zstd22 to zstd19, the kernel will > >> boot fine with below patch > >> > >> Please let me know if you need more info, and sorry for the late report > >> as we just tracked down to this point. > > > > Thanks for the report, I will look into it today. > > CC: Petr Malat > > I’ve successfully reproduced, and found the issue. It turns out that this > patch [0] from Petr Malat fixes the issue. As I mentioned in that thread, his > fix corresponds to this upstream commit [1]. Glad to know there is already a fix. > Can we get Petr's patch merged into v5.9? > > This bug only happens when the window size is > 8 MB. A non-kernel workaround > would be to compress the kernel level 19 instead of level 22, which uses an > 8 MB window size, instead of a 128 MB window size. > > The reason it only shows up for large kernels, is that the code is only buggy > when an offset > 8 MB is used, so a kernel <= 8 MB can't trigger the bug. > > Best, > Nick > > [0] https://lkml.org/lkml/2020/9/14/94 With this patch, all the failed cases on my side could boot fine. Tested-by: Feng Tang <feng.tang@xxxxxxxxx> Thanks, Feng > [1] https://github.com/facebook/zstd/commit/8a5c0c98ae5a7884694589d7a69bc99011add94d
