Re: raid6 badness

From: H. Peter Anvin (hpa_at_zytor.com)
Date: 01/31/04

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    To: linux-kernel@vger.kernel.org
Date:	Sat, 31 Jan 2004 02:13:09 +0000 (UTC)

    Followup to: <Pine.LNX.4.58.0401301158340.8900@sapphire.newearth.org>
    By author: "Michael V. David" <michael@mvdavid.com>
    In newsgroup: linux.dev.kernel
    >
    > This x86_64 system has dual Opteron CPUs on a Tyan 2880 board. Kernel
    > version string:
    >
    > Linux version 2.6.2-bk4 (michael@sapphire) (gcc version 3.3.2 20040119 (Red Hat Linux 3.3.2-8)) #3 SMP Fri Jan 30
    > 08:56:11 EST 2004
    >
    > The same problem was produced with kernel versions 2.6.2-rc2 and
    > 2.6.2-rc2-bk4. Output reproduced here is from -bk4.
    >
    > If raid6 is compiled into the kernel, the kernel panics while
    > starting. In the present case, it was compiled as a module. On
    > loading, there is a segfault, and syslog gets what follows:
    >
    > ---<snip>---
    > raid6: int64x1 1175 MB/s
    > raid6: int64x2 1734 MB/s
    > raid6: int64x4 1773 MB/s
    > raid6: int64x8 1273 MB/s
    > general protection fault: 0000 [1]
    > CPU 1
    > Pid: 7310, comm: modprobe Not tainted
    > RIP: 0010:[<ffffffffa0186383>] <ffffffffa0186383>{:raid6:raid6_sse21_gen_syndrome+51}
    > RSP: 0018:0000010021825dd8 EFLAGS: 00010202
                               ^
                               
    It crashes because the stack is misaligned. x86-64 requires that the
    stack is always aligned to a 16-byte boundary, but your stack pointer
    isn't.

    The RAID-6 code for x86-64 specifically assumes proper stack
    alignment, so a misaligned stack is fatal.

    I don't know what would cause the stack to be misaligned, however.

            -hpa
    -
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