Messages in this thread | | | Date | Wed, 23 Feb 2011 13:40:17 -0500 | From | Mathieu Desnoyers <> | Subject | Re: [PATCH] debug rcu head support !PREEMPT config |
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* Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote: > On Wed, Feb 23, 2011 at 10:37:26AM -0500, Mathieu Desnoyers wrote: > > * Steven Rostedt (rostedt@goodmis.org) wrote: > > > On Wed, 2011-02-23 at 10:13 -0500, Mathieu Desnoyers wrote: > > > > Remove DEBUG_RCU_HEAD dependency on PREEMPT config. Handle the unability to > > > > detect if within a RCU read-side critical section by never performing any > > > > attempt to recover from a failure situation in the fixup handlers. Just print > > > > the warnings. > > > > > > > > This patch is only compile-tested. > > > > > > > > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > > > > --- > > > > kernel/rcupdate.c | 17 +++++++++++++++++ > > > > lib/Kconfig.debug | 2 +- > > > > 2 files changed, 18 insertions(+), 1 deletion(-) > > > > > > > > Index: linux-2.6-lttng/lib/Kconfig.debug > > > > =================================================================== > > > > --- linux-2.6-lttng.orig/lib/Kconfig.debug > > > > +++ linux-2.6-lttng/lib/Kconfig.debug > > > > @@ -313,7 +313,7 @@ config DEBUG_OBJECTS_WORK > > > > > > > > config DEBUG_OBJECTS_RCU_HEAD > > > > bool "Debug RCU callbacks objects" > > > > - depends on DEBUG_OBJECTS && PREEMPT > > > > + depends on DEBUG_OBJECTS > > > > help > > > > Enable this to turn on debugging of RCU list heads (call_rcu() usage). > > > > > > > > Index: linux-2.6-lttng/kernel/rcupdate.c > > > > =================================================================== > > > > --- linux-2.6-lttng.orig/kernel/rcupdate.c > > > > +++ linux-2.6-lttng/kernel/rcupdate.c > > > > @@ -142,7 +142,14 @@ static int rcuhead_fixup_init(void *addr > > > > * Ensure that queued callbacks are all executed. > > > > * If we detect that we are nested in a RCU read-side critical > > > > * section, we should simply fail, otherwise we would deadlock. > > > > + * In !PREEMPT configurations, there is no way to tell if we are > > > > + * in a RCU read-side critical section or not, so we never > > > > + * attempt any fixup and just print a warning. > > > > */ > > > > +#ifndef CONFIG_PREEMPT > > > > + WARN_ON(1); > > > > + return 0; > > > > +#endif > > > > if (rcu_preempt_depth() != 0 || preempt_count() != 0 || > > > > irqs_disabled()) { > > > > WARN_ON(1); > > > > @@ -184,7 +191,14 @@ static int rcuhead_fixup_activate(void * > > > > * Ensure that queued callbacks are all executed. > > > > * If we detect that we are nested in a RCU read-side critical > > > > * section, we should simply fail, otherwise we would deadlock. > > > > + * In !PREEMPT configurations, there is no way to tell if we are > > > > + * in a RCU read-side critical section or not, so we never > > > > + * attempt any fixup and just print a warning. > > > > */ > > > > +#ifndef CONFIG_PREEMPT > > > > + WARN_ON(1); > > > > + return 0; > > > > +#endif > > > > if (rcu_preempt_depth() != 0 || preempt_count() != 0 || > > > > irqs_disabled()) { > > > > WARN_ON(1); > > > > @@ -214,6 +228,9 @@ static int rcuhead_fixup_free(void *addr > > > > * Ensure that queued callbacks are all executed. > > > > * If we detect that we are nested in a RCU read-side critical > > > > * section, we should simply fail, otherwise we would deadlock. > > > > + * In !PREEMPT configurations, there is no way to tell if we are > > > > + * in a RCU read-side critical section or not, so we never > > > > + * attempt any fixup and just print a warning. > > > > */ > > > > #ifndef CONFIG_PREEMPT > > > > WARN_ON(1); > > > > > > Hmm, I wonder if s/WARN_ON/WARN_ON_ONCE/g is in order. Why spam the > > > console if it happens to trigger all the time? > > > > The system should die pretty soon anyway due to list corruption, so I > > don't think it's a problem in practice. > > Well, it would add noise, so I added a patch converting the WARN_ON's > to WARN_ON_ONCE's.
Thinking about it, it makes a lot of sense. Thanks!
Mathieu
-- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com
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