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    SubjectRe: [x86] BUG: unable to handle kernel paging request at 00740060
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    On Sat, Oct 5, 2013 at 4:44 PM, Fengguang Wu <fengguang.wu@intel.com> wrote:
    >
    > I got the below dmesg and the first bad commit is
    >
    > commit 0c44c2d0f459 ("x86: Use asm goto to implement better modify_and_test() functions"

    Hmm. I'm looking at the final version of that patch, and I'm not
    seeing anything wrong. It may trigger a compiler bug - there aren't
    that many "asm goto" users, and using them for the bitops adds a lot
    of new cases.

    Your oops makes very little sense, it looks like task_work_run() just
    called out to random crap, probably because the work was already
    released, so "work->func()" ends up being bad. I'm adding Oleg to the
    participants anyway, just in case there is some race. The comment says
    that it can race with task_work_cancel() playing with *work. Oleg,
    comments?

    However, I don't see any actual bit-op code in task_work_run() itself,
    so it's something else that got miscompiled and corrupted memory. In
    that respect, the oops you have looks more like the oopses you got
    with DEBUG_KOBJECT_RELEASE. Are you sure that wasn't set?

    That said, Fengguang, can you try two things just to check:

    - add "cc" to the clobbers list for the asm goto (technically it
    should be on the non-asm-goto as well, but we never had that, and
    maybe the fact that gcc always ends up testing a register afterwards
    hides the need for the clobber).

    So it would look like this in arch/x86/include/asm/rmwcc.h

    #define __GEN_RMWcc(fullop, var, cc, ...) \
    do { \
    asm volatile goto (fullop "; j" cc " %l[cc_label]" \
    : : "m" (var), ## __VA_ARGS__ \
    : "memory", "cc" : cc_label); \
    return 0; \
    cc_label: \
    return 1; \

    (where that "cc" thing is new). I'm not sure if "cc" really matters on
    x86 at all (it didn't use to, long long ago), but maybe it does these
    days..

    If that makes no difference, please just verify that the non-asm-goto
    version works fine, by changing the

    #ifdef CC_HAVE_ASM_GOTO

    into a simple "#if 0" to disable the asm-goto version.

    Linus


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