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    SubjectRe: [debug patch] printk: Add a printk killswitch to robustify NMI watchdog messages

    * Arne Jansen <lists@die-jansens.de> wrote:

    > On 06.06.2011 19:11, Ingo Molnar wrote:
    > >
    > >* Peter Zijlstra<peterz@infradead.org> wrote:
    >
    > >
    > >>+void printk_tick(void)
    > >>+{
    > >>+ if (!__this_cpu_read(printk_pending))
    > >>+ return;
    > >>+
    > >>+ /*
    > >>+ * Try to acquire and then immediately release the
    > >>+ * console semaphore. The release will do all the
    > >>+ * actual magic (print out buffers, wake up klogd,
    > >>+ * etc).
    > >>+ */
    > >>+ if (console_trylock_for_printk(smp_processor_id())) {
    > >>+ console_unlock();
    > >>+ __this_cpu_write(printk_pending, 0);
    > >>+ }
    > >>+}
    > >
    > >Arne does this fix the hang you are seeing?
    >
    > What do you want me to test? just replace printk_tick with the
    > above version? If I do that, the machine doesn't even boot up any
    > more.

    Yeah.

    So i think we want two patches:

    - The first one that minimally removes the lockdep_off()/on() dance
    and fixes the regression: the patch that i sent earlier today.
    I *think* that should fix the crash.

    3.0 material.

    - The second one that moves console_sem wakeups to the jiffies tick.
    It does not push the acquiring and the console->write() calls to
    jiffies context, only delays the wakeup.

    3.1 material.

    Thanks,

    Ingo


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