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    SubjectRe: debugctl msr

    On Wed, Nov 19, 2008 at 7:27 PM, Markus Metzger
    <> wrote:
    > On Wed, 2008-11-19 at 18:13 +0100, stephane eranian wrote:
    >> I found another issue with ds_release(). You need to skip freeing the
    >> buffer when it
    >> is NULL, i.e., was already allocated by caller of ds_request_pebs().
    > ds_release() is not robust with respect to double release, if that's
    > what you mean. Is that desirable?
    I don't think so.

    > For a single ds_release() call matching a corresponding successful
    > ds_request() call, the buffer is freed if and only if it had been
    > allocated by ds.c.
    > Kfree() itself handles NULL pointers and scripts/ warns on
    > a check for NULL around a kfree() call.
    Yes, I have narrowed this down to the following lines:
    current->mm->total_vm -= context->pages[qual];
    current->mm->locked_vm -= context->pages[qual];

    I think this is again related to the problem of which thread call
    ds_release(). In my test
    case, this is the monitored thread as it exits. By the time it gets
    there current->mm is NULL.

    >> As for handling the interrupt is ds.c, not clear how this could work
    >> with current perfmon.
    >> I don't know how this work on the BTS side. On the PMU side, that is not because
    >> I am using PEBS, that I don't also use other counters as well. Longer
    >> term, I think, there
    >> needs to be a lower-level PMU interrupt service where you would
    >> register a callback
    >> on PMU interrupts. It would be used by NMI watchdog, perfmon,
    >> Oprofile, ds.c.
    > That's even preferable to having the interrupt code itself in ds.c

    > The point I was trying to make is that buffer overflows should not be
    > handled on higher levels (i.e. users of ds.c). That's why I am so
    > reluctant to expose the interrupt threshold in the ds.c interface.
    But the threshold is a characteristic of the buffer, not the interrupt handler.
    Depending on the tool, it may be interesting to set the threshold earlier than
    at the end of the buffer.

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      Last update: 2008-11-19 20:23    [W:0.044 / U:9.944 seconds]
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