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    SubjectRe: [RFC] [PATCH] cpuset operations causes Badness at mm/slab.c:777 warning
    > The allocated array has 0 bytes. Any dereference is an error.

    Well, then, that doesn't work either.

    We -agree- we can't have this failing. You suggested (if I understood
    correctly, which I doubt) that we set the pointer to NULL, and noted
    that derefencing a NULL pointer would fail. I agree such derefences
    would fail, and tried to point out that this would be bad. We can't
    have pointer dereferences failing in the kernel ... duh.

    Your reply seems like a non sequiter to me, pointing out that having
    a pointer to an array of 0 bytes fails as well. Ok - that's bad too.

    So we cannot have a NULL pointer, used unchecked, and we cannot have
    a non-NULL pointer to a zero byte array, used unchecked.

    As I said, and as I thought Srinivasa coded, with these patch lines:

    @@ -1772,6 +1779,9 @@ static ssize_t cpuset_tasks_read(struct
    struct ctr_struct *ctr = file->private_data;

    + if (!ctr->buf) /* No tasks in this cpuset */
    + return 0;
    return simple_read_from_buffer(buf, nbytes, ppos, ctr->buf, ctr->bufsz);

    we actually have to check the NULL-ness (or emptiness) of this thing,
    down where it would be used, to avoid using NULL or empty things.

    Summary - Srinivasa's patch still looks ok to me. This followup
    discussion between you and I is just confusing me - sorry.

    I won't rest till it's the best ...
    Programmer, Linux Scalability
    Paul Jackson <> 1.925.600.0401
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      Last update: 2007-06-01 21:51    [W:0.022 / U:15.036 seconds]
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