diff mbox series

[v3,7/7] rcu: Add CONFIG_RCU_SR_NORMAL_DEBUG_GP

Message ID 20231128080033.288050-8-urezki@gmail.com
State New
Headers
Series Reduce synchronize_rcu() latency(V3) |

Commit Message

Uladzislau Rezki Nov. 28, 2023, 8 a.m. UTC 
  This option enables additional debugging for detecting a grace
period incompletion for synchronize_rcu() users. If a GP is not
fully passed for any user, the warning message is emitted.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
 kernel/rcu/Kconfig.debug | 12 ++++++++++++
 kernel/rcu/tree.c        |  7 +++++--
 2 files changed, 17 insertions(+), 2 deletions(-)

Comments

Paul E. McKenney Dec. 20, 2023, 1:14 a.m. UTC | #1 
On Tue, Nov 28, 2023 at 09:00:33AM +0100, Uladzislau Rezki (Sony) wrote:
> This option enables additional debugging for detecting a grace
> period incompletion for synchronize_rcu() users. If a GP is not
> fully passed for any user, the warning message is emitted.
> 
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

Much better, thank you, as this avoids the possibility of false positives
in production.  But to avoid potential bisection issues, could you please
fold this into the first patch?

							Thanx, Paul

> ---
>  kernel/rcu/Kconfig.debug | 12 ++++++++++++
>  kernel/rcu/tree.c        |  7 +++++--
>  2 files changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
> index 2984de629f74..3d44106ca1f0 100644
> --- a/kernel/rcu/Kconfig.debug
> +++ b/kernel/rcu/Kconfig.debug
> @@ -143,4 +143,16 @@ config RCU_STRICT_GRACE_PERIOD
>  	  when looking for certain types of RCU usage bugs, for example,
>  	  too-short RCU read-side critical sections.
>  
> +config RCU_SR_NORMAL_DEBUG_GP
> +	bool "Debug synchronize_rcu() callers for a grace period completion"
> +	depends on DEBUG_KERNEL && RCU_EXPERT
> +	default n
> +	help
> +	  This option enables additional debugging for detecting a grace
> +	  period incompletion for synchronize_rcu() users. If a GP is not
> +	  fully passed for any user, the warning message is emitted.
> +
> +	  Say Y here if you want to enable such debugging
> +	  Say N if you are unsure.
> +
>  endmenu # "RCU Debugging"
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index c0d3e46730e8..421bce4b8dd7 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1547,7 +1547,8 @@ static void rcu_sr_normal_complete(struct llist_node *node)
>  		(struct rcu_head *) node, struct rcu_synchronize, head);
>  	unsigned long oldstate = (unsigned long) rs->head.func;
>  
> -	WARN_ONCE(!rcu_gp_is_expedited() && !poll_state_synchronize_rcu(oldstate),
> +	WARN_ONCE(IS_ENABLED(CONFIG_RCU_SR_NORMAL_DEBUG_GP) &&
> +		!poll_state_synchronize_rcu(oldstate),
>  		"A full grace period is not passed yet: %lu",
>  		rcu_seq_diff(get_state_synchronize_rcu(), oldstate));
>  
> @@ -3822,7 +3823,9 @@ static void synchronize_rcu_normal(void)
>  	 * This code might be preempted, therefore take a GP
>  	 * snapshot before adding a request.
>  	 */
> -	rs.head.func = (void *) get_state_synchronize_rcu();
> +	if (IS_ENABLED(CONFIG_RCU_SR_NORMAL_DEBUG_GP))
> +		rs.head.func = (void *) get_state_synchronize_rcu();
> +
>  	rcu_sr_normal_add_req(&rs);
>  
>  	/* Kick a GP and start waiting. */
> -- 
> 2.39.2
>
Uladzislau Rezki Dec. 21, 2023, 10:27 a.m. UTC | #2 
> On Tue, Nov 28, 2023 at 09:00:33AM +0100, Uladzislau Rezki (Sony) wrote:
> > This option enables additional debugging for detecting a grace
> > period incompletion for synchronize_rcu() users. If a GP is not
> > fully passed for any user, the warning message is emitted.
> > 
> > Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> 
> Much better, thank you, as this avoids the possibility of false positives
> in production.  But to avoid potential bisection issues, could you please
> fold this into the first patch?
> 
Makes sense. I will fold it into the first one!

--
Uladzislau Rezki
diff mbox series

Patch

diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 2984de629f74..3d44106ca1f0 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -143,4 +143,16 @@  config RCU_STRICT_GRACE_PERIOD
 	  when looking for certain types of RCU usage bugs, for example,
 	  too-short RCU read-side critical sections.
 
+config RCU_SR_NORMAL_DEBUG_GP
+	bool "Debug synchronize_rcu() callers for a grace period completion"
+	depends on DEBUG_KERNEL && RCU_EXPERT
+	default n
+	help
+	  This option enables additional debugging for detecting a grace
+	  period incompletion for synchronize_rcu() users. If a GP is not
+	  fully passed for any user, the warning message is emitted.
+
+	  Say Y here if you want to enable such debugging
+	  Say N if you are unsure.
+
 endmenu # "RCU Debugging"
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index c0d3e46730e8..421bce4b8dd7 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1547,7 +1547,8 @@  static void rcu_sr_normal_complete(struct llist_node *node)
 		(struct rcu_head *) node, struct rcu_synchronize, head);
 	unsigned long oldstate = (unsigned long) rs->head.func;
 
-	WARN_ONCE(!rcu_gp_is_expedited() && !poll_state_synchronize_rcu(oldstate),
+	WARN_ONCE(IS_ENABLED(CONFIG_RCU_SR_NORMAL_DEBUG_GP) &&
+		!poll_state_synchronize_rcu(oldstate),
 		"A full grace period is not passed yet: %lu",
 		rcu_seq_diff(get_state_synchronize_rcu(), oldstate));
 
@@ -3822,7 +3823,9 @@  static void synchronize_rcu_normal(void)
 	 * This code might be preempted, therefore take a GP
 	 * snapshot before adding a request.
 	 */
-	rs.head.func = (void *) get_state_synchronize_rcu();
+	if (IS_ENABLED(CONFIG_RCU_SR_NORMAL_DEBUG_GP))
+		rs.head.func = (void *) get_state_synchronize_rcu();
+
 	rcu_sr_normal_add_req(&rs);
 
 	/* Kick a GP and start waiting. */