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SubjectRe: [PATCH] debug rcu head support !PREEMPT config
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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?

-- Steve




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