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    SubjectRe: [GIT PULL] updates for oprofile
    Ingo, et al., 

    Regarding today's pulled request, containing:

    commit bc078e4eab65f11bbaeed380593ab8151b30d703
    Author: Martin Schwidefsky <schwidef...@de.ibm.com>
    Date: Tue Mar 2 16:01:10 2010 +0100

    oprofile: convert oprofile from timer_hook to hrtimer


    Information is a touch scant, as I'm doing the investigation as I
    write, but I believe that that patch can cause ooops regressions
    via a null-pointer dereference in oprofile_add_sample().

    That function declares:
    """
    /**
    * Add a sample. This may be called from any context.
    */
    void oprofile_add_sample(struct pt_regs * const regs, unsigned long event);
    """

    And begins:
    """
    void oprofile_add_sample(struct pt_regs * const regs, unsigned long event)
    {
    int is_kernel = !user_mode(regs);
    """

    Where on at least two major architectures (Arm, x86), user_mode()
    unconditionally dereferences its parameter.

    Now oprofile_add_sample() is called from this context:
    """
    static enum hrtimer_restart oprofile_hrtimer_notify(struct hrtimer *hrtimer)
    {
    oprofile_add_sample(get_irq_regs(), 0);
    """

    And get_irq_regs() is NULL when not in an IRQ context.

    Bang.

    An example of this kind of thing kicking in has already been encountered
    last year:
    http://www.mail-archive.com/linux-omap@vger.kernel.org/msg14069.html
    (That thread got a little side-tracked onto OMAP specifics, but the
    original report is topical.)

    Now would be a very good time for the "many eyes" principle to kick in.

    I'm now looking into workarounds, but nothing that I'd necessarily
    want to submit as a real fix.

    Phil
    cc:'d replies appreciated


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