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    SubjectRe: [PATCH -v2] ring-buffer: add paranoid checks for loops

    * Steven Rostedt <rostedt@goodmis.org> wrote:

    > + /*
    > + * This should normally only loop twice. But because the
    > + * start of the reader inserts an empty page, it causes
    > + * a case where we will loop three times. There should be no
    > + * reason to loop four times (that I know of).
    > + */
    > + if (unlikely(paranoid > 2)) {
    > + RB_WARN_ON(cpu_buffer, 1);
    > + reader = NULL;
    > + goto out;
    > + }
    > + paranoid++;

    ok, the explanations look nice now.

    A small nit - the above comment suggests that looping 4 times is the
    anomaly - still the test is for paranoid > 2 ?

    > + int paranoid = 0;

    another small nit: i'd suggest to rename 'paranoid' to 'nr_loops' or
    'nr_iterations' or so. It is the _condition_ that signals paranoia,
    not the variable in itself - making the current patch look a bit
    weird.

    > again:
    > + /*
    > + * We repeat when a timestamp is encountered. It is possible
    > + * to get multiple timestamps from an interrupt entering just
    > + * as one timestamp is about to be written. The max times
    > + * that this can happen is the number of nested interrupts we
    > + * can have. 10 should be more than enough.
    > + */
    > + if (unlikely(paranoid > 10)) {
    > + RB_WARN_ON(cpu_buffer, 1);
    > + return NULL;

    s/10 should be more than enough/Nesting higher than 10 is clearly
    anomalous/

    > + /*
    > + * We repeat when a timestamp is encountered. It is possible
    > + * to get multiple timestamps from an interrupt entering just
    > + * as one timestamp is about to be written. The max times
    > + * that this can happen is the number of nested interrupts we
    > + * can have. 10 should be more than enough.
    > + */
    > + if (unlikely(paranoid > 10)) {
    > + RB_WARN_ON(cpu_buffer, 1);
    > + return NULL;

    ditto.

    Ingo


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