Messages in this thread | | | Date | Wed, 18 Nov 2009 22:59:43 -0500 | From | Masami Hiramatsu <> | Subject | Re: [PATCH] notifier atomic call chain notrace |
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Mathieu Desnoyers wrote: > * Jason Baron (jbaron@redhat.com) wrote: >> Note that this is conditional on gcc >= 4.5. Also there is a !lockdep >> condition. This is b/c the die_notifier takes an rcu_read_lock() on the >> int3 trap, which then causes another one etc. Since, we aren't going to be >> installing removing the handler, the rcu_read_lock() could be avoided for this >> case with some code restructuring. >> > [snip] > > Would the following patch help ? I use it in the LTTng tree to alleviate > this problem.
Reviewed-by: Masami Hiramatsu <mhiramat@redhat.com>
The code itself seems OK for me. :-)
I'd just like to hear the opinion from Ingo, since this change will change all atomic-notifier's locks to notrace.
> notifier atomic call chain notrace > > In LTTng, being able to use the atomic notifier from cpu idle entry to > ensure the tracer flush the last events in the current subbuffer > requires the rcu read-side to be marked "notrace", otherwise it can end > up calling back into lockdep and the tracer. > > Also apply to the the die notifier. > > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> > CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > CC: Jason Baron <jbaron@redhat.com> > CC: mingo@elte.hu > --- > kernel/notifier.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > Index: linux-2.6-lttng/kernel/notifier.c > =================================================================== > --- linux-2.6-lttng.orig/kernel/notifier.c 2009-11-12 17:58:56.000000000 -0500 > +++ linux-2.6-lttng/kernel/notifier.c 2009-11-12 18:03:28.000000000 -0500 > @@ -148,7 +148,7 @@ int atomic_notifier_chain_unregister(str > spin_lock_irqsave(&nh->lock, flags); > ret = notifier_chain_unregister(&nh->head, n); > spin_unlock_irqrestore(&nh->lock, flags); > - synchronize_rcu(); > + synchronize_sched(); > return ret; > } > EXPORT_SYMBOL_GPL(atomic_notifier_chain_unregister); > @@ -178,9 +178,9 @@ int __kprobes __atomic_notifier_call_cha > { > int ret; > > - rcu_read_lock(); > + rcu_read_lock_sched_notrace(); > ret = notifier_call_chain(&nh->head, val, v, nr_to_call, nr_calls); > - rcu_read_unlock(); > + rcu_read_unlock_sched_notrace(); > return ret; > } > EXPORT_SYMBOL_GPL(__atomic_notifier_call_chain); >
-- Masami Hiramatsu
Software Engineer Hitachi Computer Products (America), Inc. Software Solutions Division
e-mail: mhiramat@redhat.com
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