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    SubjectRe: [PATCH 01/20 -v5] printk - dont wakeup klogd with interrupts disabled
    On Wed 2008-01-23 12:27:12, Steven Rostedt wrote:
    >
    > On Wed, 23 Jan 2008, Daniel Walker wrote:
    >
    > >
    > > On Wed, 2008-01-23 at 11:02 -0500, Steven Rostedt wrote:
    > >
    > > > + if (!irqs_disabled() && wake_klogd)
    > > > wake_up_klogd();
    > >
    > > This causes a regression .. When printk is called during an OOPS in
    > > kernels without this change then the OOPS will get logged, since the
    > > logging process (klogd) is woken to handle the messages.. If you apply
    > > this change klogd doesn't wakeup, and hence doesn't log the oops.. So if
    > > you remove the wakeup here you have to add it someplace else to maintain
    > > the logging ..
    > >
    > > (I'm not theorizing here, I have defects logged against this specific
    > > piece of code..)
    >
    > It wont get woken up anyway. Did you look at wake_up_klogd?
    >
    > void wake_up_klogd(void)
    > {
    > if (!oops_in_progress && waitqueue_active(&log_wait))
    > wake_up_interruptible(&log_wait);
    > }
    >
    >
    > So if oops_in_progress is set, then it still wont get woken. Perhaps it
    > got woken some other way? Or is oops_in_progress not set in these oops?
    >
    > One other solution is to make the runqueue locks visible externally. Like:
    >
    > in sched.c:
    >
    > int runqueue_is_locked(void)
    > {
    > int cpu = get_cpu();
    > struct rq *rq = cpu_rq(cpu);
    > int ret;
    >
    > ret = spin_is_locked(&rq->lock);
    > put_cpu();
    > return ret;
    > }
    >
    > And in printk we could do:
    >
    > if (wake_klogd && !runqueue_is_locked())
    > wake_up_klogd();
    >
    > This probably is the cleanest solution since it simply prevents the
    > deadlock from occurring.

    Yes please... this looks like a solution to me.
    Pavel
    --
    (english) http://www.livejournal.com/~pavelmachek
    (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


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