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    SubjectRe: [PATCH 0/5] [GIT PULL] updates for tip/tracing/ftrace
    On Fri, Mar 20, 2009 at 08:54:14PM +0100, Ingo Molnar wrote:
    >
    > * Frederic Weisbecker <fweisbec@gmail.com> wrote:
    >
    > > On Fri, Mar 20, 2009 at 08:27:21PM +0100, Ingo Molnar wrote:
    > > >
    > > > * Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
    > > >
    > > > > On Fri, Mar 20, 2009 at 07:38:49PM +0100, Ingo Molnar wrote:
    > > > > >
    > > > > > * Ingo Molnar <mingo@elte.hu> wrote:
    > > > > >
    > > > > > > > > This looks like it is RCU/stop_machine related. The CPU is
    > > > > > > > > stuck in in stop_machine? I see that rcu_torture is running.
    > > > > > > > > Does this go away if you turn off rcu_torture?
    > > > > > > >
    > > > > > > > Grasping at straws... Does Lai's rcu_barrier() fix help?
    > > > > > >
    > > > > > > which one is that?
    > > > > >
    > > > > > ok, found it. Will know in about ~24 hours whether it helps.
    > > > >
    > > > > http://lkml.org/lkml/2009/3/20/71 was the one I was thinking of,
    > > > > just to double-check.
    > > >
    > > > Yeah - i just picked it up into tip:core/rcu.
    > > >
    > > > I didnt immediately connect the two things, as 'tracer self-test'
    > > > does not lend itself to 'CPU hotplug and RCU race fix' - but indeed
    > > > in the case of the function tracer there's a dependency due to
    > > > stop_machine_run(). Thanks for point it out!
    > > >
    > > > Ingo
    > >
    > >
    > > I've successfully triggered a crash, the problem is that I can't be sure this is
    > > the same because I don't have a serial line on my x86-64, and the trace goes too far.
    > > Moreover boot_delay=N make it disappear.
    > >
    > > I can trigger it each time I boot with ftrace=function_graph and
    > > the following patch applied:
    > >
    > > diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
    > > index 7c4142a..e9914a8 100644
    > > --- a/kernel/rcutorture.c
    > > +++ b/kernel/rcutorture.c
    > > @@ -616,7 +616,7 @@ rcu_torture_writer(void *arg)
    > > static DEFINE_RCU_RANDOM(rand);
    > >
    > > VERBOSE_PRINTK_STRING("rcu_torture_writer task started");
    > > - set_user_nice(current, 19);
    > > + set_user_nice(current, -1);
    > >
    > > do {
    > > schedule_timeout_uninterruptible(1);
    > > @@ -736,7 +736,7 @@ rcu_torture_reader(void *arg)
    > > struct timer_list t;
    > >
    > > VERBOSE_PRINTK_STRING("rcu_torture_reader task started");
    > > - set_user_nice(current, 19);
    > > + set_user_nice(current, -1);
    > > if (irqreader && cur_ops->irqcapable)
    > > setup_timer_on_stack(&t, rcu_torture_timer, 0);
    >
    > i dont have a reproducer right now. Can you trigger it with latest
    > -tip, which has this commit included:
    >
    > 04cb9ac: rcu: rcu_barrier VS cpu_hotplug: Ensure callbacks in dead cpu are migrated to o
    >
    > ?
    >
    > Ingo


    I tested three times the same things but with 04cb9ac and... it didn't triggered
    anymore :-)



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