And speaking of avoiding inconveniencing users...

And speaking of avoiding inconveniencing users...

[Paul E. McKenney]

Hello, Uladzislau,

And I wasn't paying attention when reviewing this patch:

084e1c049a8e ("rcu: Introduce CONFIG_RCU_EXP_CPU_STALL_TIMEOUT")

Distros specifying 60 seconds for the stall timeout get hit with a silent
change to 21 seconds for the expedited stall timeout.

Unless you tell me otherwise, I will merge the following diff into the
above commit.  So please let me know if this will cause any problems.

							Thanx, Paul

------------------------------------------------------------------------

diff --git a/Documentation/RCU/stallwarn.rst b/Documentation/RCU/stallwarn.rst
index 1d863b04727c3..794837eb519b9 100644
--- a/Documentation/RCU/stallwarn.rst
+++ b/Documentation/RCU/stallwarn.rst
@@ -166,10 +166,12 @@ CONFIG_RCU_EXP_CPU_STALL_TIMEOUT
 --------------------------------
 
 	Same as the CONFIG_RCU_CPU_STALL_TIMEOUT parameter but only for
-	the expedited grace period. This parameter defines the period of
-	time that RCU will wait from the beginning of an expedited grace
-	period until it issues an RCU CPU stall warning. This time period
-	is normally 20 milliseconds on Android devices.
+	the expedited grace period. This parameter defines the period
+	of time that RCU will wait from the beginning of an expedited
+	grace period until it issues an RCU CPU stall warning. This time
+	period is normally 20 milliseconds on Android devices.	A zero
+	value causes the CONFIG_RCU_CPU_STALL_TIMEOUT value to be used,
+	after conversion to milliseconds.
 
 	This configuration parameter may be changed at runtime via the
 	/sys/module/rcupdate/parameters/rcu_exp_cpu_stall_timeout, however
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 34d44648f3f5d..ca9db809beda3 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4936,6 +4936,9 @@
 			and the maximum allowed value is 21000
 			milliseconds. Please note that this value is
 			adjusted to an arch timer tick resolution.
+			Setting this to zero causes the value from
+			rcupdate.rcu_cpu_stall_timeout to be used (after
+			conversion from seconds to milliseconds).
 
 	rcupdate.rcu_expedited= [KNL]
 			Use expedited grace-period primitives, for
diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 39dd4b9d647f8..9b64e55d4f615 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -85,15 +85,16 @@ config RCU_CPU_STALL_TIMEOUT
 config RCU_EXP_CPU_STALL_TIMEOUT
 	int "Expedited RCU CPU stall timeout in milliseconds"
 	depends on RCU_STALL_COMMON
-	range 1 21000
+	range 0 21000
 	default 20 if ANDROID
-	default 21000 if !ANDROID
-
+	default 0 if !ANDROID
 	help
 	  If a given expedited RCU grace period extends more than the
 	  specified number of milliseconds, a CPU stall warning is printed.
 	  If the RCU grace period persists, additional CPU stall warnings
-	  are printed at more widely spaced intervals.
+	  are printed at more widely spaced intervals.  A value of zero
+	  says to use the RCU_CPU_STALL_TIMEOUT value converted from
+	  seconds to milliseconds.
 
 config RCU_TRACE
 	bool "Enable tracing for RCU"
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 0a25a4ea6eef8..2464b0eccfd02 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -31,15 +31,17 @@ int rcu_exp_jiffies_till_stall_check(void)
 	int exp_stall_delay_delta = 0;
 	int till_stall_check;
 
-	/*
-	 * Limit check must be consistent with the Kconfig limits for
-	 * CONFIG_RCU_EXP_CPU_STALL_TIMEOUT, so check the allowed range.
-	 * The minimum clamped value is "2UL", because at least one full
-	 * tick has to be guaranteed.
-	 */
+	// Zero says to use rcu_cpu_stall_timeout, but in milliseconds.
+	if (!cpu_stall_timeout)
+		cpu_stall_timeout = jiffies_to_msecs(rcu_jiffies_till_stall_check());
+
+	// Limit check must be consistent with the Kconfig limits for
+	// CONFIG_RCU_EXP_CPU_STALL_TIMEOUT, so check the allowed range.
+	// The minimum clamped value is "2UL", because at least one full
+	// tick has to be guaranteed.
 	till_stall_check = clamp(msecs_to_jiffies(cpu_stall_timeout), 2UL, 21UL * HZ);
 
-	if (jiffies_to_msecs(till_stall_check) != cpu_stall_timeout)
+	if (cpu_stall_timeout && jiffies_to_msecs(till_stall_check) != cpu_stall_timeout)
 		WRITE_ONCE(rcu_exp_cpu_stall_timeout, jiffies_to_msecs(till_stall_check));
 
 #ifdef CONFIG_PROVE_RCU

Re: And speaking of avoiding inconveniencing users...

[Uladzislau Rezki]

Hello, Paul.

Indeed the changed switched to 21 seconds. What is about just set the
60 000 for !ANDROID?

default 60000 if !ANDROID

On Mon, May 9, 2022 at 10:58 PM Paul E. McKenney <paulmck@kernel.org> wrote:
>
> Hello, Uladzislau,
>
> And I wasn't paying attention when reviewing this patch:
>
> 084e1c049a8e ("rcu: Introduce CONFIG_RCU_EXP_CPU_STALL_TIMEOUT")
>
> Distros specifying 60 seconds for the stall timeout get hit with a silent
> change to 21 seconds for the expedited stall timeout.
>
> Unless you tell me otherwise, I will merge the following diff into the
> above commit.  So please let me know if this will cause any problems.
>
>                                                         Thanx, Paul
>
> ------------------------------------------------------------------------
>
> diff --git a/Documentation/RCU/stallwarn.rst b/Documentation/RCU/stallwarn.rst
> index 1d863b04727c3..794837eb519b9 100644
> --- a/Documentation/RCU/stallwarn.rst
> +++ b/Documentation/RCU/stallwarn.rst
> @@ -166,10 +166,12 @@ CONFIG_RCU_EXP_CPU_STALL_TIMEOUT
>  --------------------------------
>
>         Same as the CONFIG_RCU_CPU_STALL_TIMEOUT parameter but only for
> -       the expedited grace period. This parameter defines the period of
> -       time that RCU will wait from the beginning of an expedited grace
> -       period until it issues an RCU CPU stall warning. This time period
> -       is normally 20 milliseconds on Android devices.
> +       the expedited grace period. This parameter defines the period
> +       of time that RCU will wait from the beginning of an expedited
> +       grace period until it issues an RCU CPU stall warning. This time
> +       period is normally 20 milliseconds on Android devices.  A zero
> +       value causes the CONFIG_RCU_CPU_STALL_TIMEOUT value to be used,
> +       after conversion to milliseconds.
>
>         This configuration parameter may be changed at runtime via the
>         /sys/module/rcupdate/parameters/rcu_exp_cpu_stall_timeout, however
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 34d44648f3f5d..ca9db809beda3 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -4936,6 +4936,9 @@
>                         and the maximum allowed value is 21000
>                         milliseconds. Please note that this value is
>                         adjusted to an arch timer tick resolution.
> +                       Setting this to zero causes the value from
> +                       rcupdate.rcu_cpu_stall_timeout to be used (after
> +                       conversion from seconds to milliseconds).
>
>         rcupdate.rcu_expedited= [KNL]
>                         Use expedited grace-period primitives, for
> diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
> index 39dd4b9d647f8..9b64e55d4f615 100644
> --- a/kernel/rcu/Kconfig.debug
> +++ b/kernel/rcu/Kconfig.debug
> @@ -85,15 +85,16 @@ config RCU_CPU_STALL_TIMEOUT
>  config RCU_EXP_CPU_STALL_TIMEOUT
>         int "Expedited RCU CPU stall timeout in milliseconds"
>         depends on RCU_STALL_COMMON
> -       range 1 21000
> +       range 0 21000
>         default 20 if ANDROID
> -       default 21000 if !ANDROID
> -
> +       default 0 if !ANDROID
>         help
>           If a given expedited RCU grace period extends more than the
>           specified number of milliseconds, a CPU stall warning is printed.
>           If the RCU grace period persists, additional CPU stall warnings
> -         are printed at more widely spaced intervals.
> +         are printed at more widely spaced intervals.  A value of zero
> +         says to use the RCU_CPU_STALL_TIMEOUT value converted from
> +         seconds to milliseconds.
>
>  config RCU_TRACE
>         bool "Enable tracing for RCU"
> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> index 0a25a4ea6eef8..2464b0eccfd02 100644
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -31,15 +31,17 @@ int rcu_exp_jiffies_till_stall_check(void)
>         int exp_stall_delay_delta = 0;
>         int till_stall_check;
>
> -       /*
> -        * Limit check must be consistent with the Kconfig limits for
> -        * CONFIG_RCU_EXP_CPU_STALL_TIMEOUT, so check the allowed range.
> -        * The minimum clamped value is "2UL", because at least one full
> -        * tick has to be guaranteed.
> -        */
> +       // Zero says to use rcu_cpu_stall_timeout, but in milliseconds.
> +       if (!cpu_stall_timeout)
> +               cpu_stall_timeout = jiffies_to_msecs(rcu_jiffies_till_stall_check());
> +
> +       // Limit check must be consistent with the Kconfig limits for
> +       // CONFIG_RCU_EXP_CPU_STALL_TIMEOUT, so check the allowed range.
> +       // The minimum clamped value is "2UL", because at least one full
> +       // tick has to be guaranteed.
>         till_stall_check = clamp(msecs_to_jiffies(cpu_stall_timeout), 2UL, 21UL * HZ);
>
> -       if (jiffies_to_msecs(till_stall_check) != cpu_stall_timeout)
> +       if (cpu_stall_timeout && jiffies_to_msecs(till_stall_check) != cpu_stall_timeout)
>                 WRITE_ONCE(rcu_exp_cpu_stall_timeout, jiffies_to_msecs(till_stall_check));
>
>  #ifdef CONFIG_PROVE_RCU



-- 
Uladzislau Rezki