[PATCH for-v7.5 12/14] rcutorture: Enable RCU

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* [PATCH for-v7.5 12/14] rcutorture: Enable RCU_BOOST where supported
       [not found] <20261113005747.2977123-1-jfern@kernel.org>
@ 2026-11-13  0:57 ` Joel Fernandes
  2026-11-14  0:58   ` sashiko-bot
  0 siblings, 1 reply; 2+ messages in thread
From: Joel Fernandes @ 2026-11-13  0:57 UTC (permalink / raw)
  To: linux-kernel, Paul E . McKenney, Frederic Weisbecker,
	Neeraj Upadhyay, Joel Fernandes, Josh Triplett, Boqun Feng,
	Uladzislau Rezki, Steven Rostedt, Mathieu Desnoyers,
	Lai Jiangshan, Zqiang, Shuah Khan, Sebastian Andrzej Siewior,
	Clark Williams
  Cc: rcu, Andrew Morton, linux-kselftest, linux-rt-devel

From: "Paul E. McKenney" <paulmck@kernel.org>

Currently, RCU_BOOST depends on RCU_EXPERT, and is therefore often
disabled in stress-test such as those run by syzbot.  This means that if
syzbot runs a test that overloads CPUs on kernels built with PREEMPT_RCU,
RCU CPU stall warnings are not unexpected.  What happens is that a
low-priority task in an RCU read-side critical section is preempted,
cannot be priority boosted, and stays that way for more than 21 seconds.

This commit therefore drops RCU_EXPERT from the RCU_BOOST "depends on"
line and removes the prompt, thus directly driving RCU_BOOST from the
kernel configuration so as to enable it anywhere it is supported and
might help.

This commit is also marked experimental because neither Ubuntu, Fedora,
nor CentOS enable RCU_BOOST.  This suggests less testing of RCU priority
boosting than one might wish.

Reported-by: Andrew Morton <akpm@linux-foundation.org>
Closes: https://lore.kernel.org/all/20260805122952.6ae38af69a0457779cb44359@linux-foundation.org/
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes <jfern@kernel.org>
---
 kernel/rcu/Kconfig                                     | 10 ++++------
 tools/testing/selftests/rcutorture/configs/rcu/NOCB01  |  1 -
 tools/testing/selftests/rcutorture/configs/rcu/NOCB02  |  1 -
 tools/testing/selftests/rcutorture/configs/rcu/TREE01  |  1 -
 tools/testing/selftests/rcutorture/configs/rcu/TREE02  |  1 -
 tools/testing/selftests/rcutorture/configs/rcu/TREE08  |  1 -
 .../testing/selftests/rcutorture/configs/rcuscale/TINY |  1 -
 .../selftests/rcutorture/configs/rcuscale/TRACE01      |  1 -
 .../testing/selftests/rcutorture/configs/rcuscale/TREE |  1 -
 .../selftests/rcutorture/configs/rcuscale/TREE54       |  1 -
 .../selftests/rcutorture/configs/refscale/NOPREEMPT    |  1 -
 .../selftests/rcutorture/configs/refscale/PREEMPT      |  1 -
 .../testing/selftests/rcutorture/configs/refscale/TINY |  1 -
 13 files changed, 4 insertions(+), 18 deletions(-)

diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index b6d3597758fc..2d0132e0a90f 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -238,17 +238,15 @@ config RCU_FANOUT_LEAF
 	  Take the default if unsure.
 
 config RCU_BOOST
-	bool "Enable RCU priority boosting"
-	depends on (RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT) || PREEMPT_RT
-	default y if PREEMPT_RT
+	bool
+	default y if (RT_MUTEXES && PREEMPT_RCU) || PREEMPT_RT
 	help
 	  This option boosts the priority of preempted RCU readers that
 	  block the current preemptible RCU grace period for too long.
 	  This option also prevents heavy loads from blocking RCU
-	  callback invocation.
+	  callback invocation.  It is now automatically enabled in
+	  any kernel that can benefit from it and that can support it.
 
-	  Say Y here if you are working with real-time apps or heavy loads
-	  Say N here if you are unsure.
 
 config RCU_BOOST_DELAY
 	int "Milliseconds to delay boosting after RCU grace-period start"
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/NOCB01 b/tools/testing/selftests/rcutorture/configs/rcu/NOCB01
index bbe6d28210ab..91ca7e8b5725 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/NOCB01
+++ b/tools/testing/selftests/rcutorture/configs/rcu/NOCB01
@@ -14,7 +14,6 @@ CONFIG_RCU_FANOUT_LEAF=2
 CONFIG_RCU_NOCB_CPU=y
 CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_PROVE_LOCKING=n
-CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
 CONFIG_RCU_EQS_DEBUG=y
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/NOCB02 b/tools/testing/selftests/rcutorture/configs/rcu/NOCB02
index 4c2b8cd6d8fd..ed3f3f7b29e7 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/NOCB02
+++ b/tools/testing/selftests/rcutorture/configs/rcu/NOCB02
@@ -14,7 +14,6 @@ CONFIG_RCU_FANOUT_LEAF=2
 CONFIG_RCU_NOCB_CPU=y
 CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_PROVE_LOCKING=n
-CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
 CONFIG_RCU_EQS_DEBUG=y
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE01 b/tools/testing/selftests/rcutorture/configs/rcu/TREE01
index 54b1600c7eb5..be5bf69a1b60 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/TREE01
+++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE01
@@ -10,6 +10,5 @@ CONFIG_RCU_TRACE=y
 CONFIG_HOTPLUG_CPU=y
 CONFIG_RCU_NOCB_CPU=y
 CONFIG_DEBUG_LOCK_ALLOC=n
-CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE02 b/tools/testing/selftests/rcutorture/configs/rcu/TREE02
index 2871ee599891..36b9228ae703 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/TREE02
+++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE02
@@ -13,7 +13,6 @@ CONFIG_RCU_FANOUT_LEAF=3
 CONFIG_RCU_NOCB_CPU=n
 CONFIG_DEBUG_LOCK_ALLOC=y
 CONFIG_PROVE_LOCKING=n
-CONFIG_RCU_BOOST=n
 CONFIG_RCU_EXPERT=y
 CONFIG_DEBUG_OBJECTS=y
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=y
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE08 b/tools/testing/selftests/rcutorture/configs/rcu/TREE08
index 8b561355b9ef..ad7d7f873e1e 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/TREE08
+++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE08
@@ -13,7 +13,6 @@ CONFIG_RCU_FANOUT_LEAF=2
 CONFIG_RCU_NOCB_CPU=y
 CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_PROVE_LOCKING=n
-CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
 CONFIG_RCU_EQS_DEBUG=y
diff --git a/tools/testing/selftests/rcutorture/configs/rcuscale/TINY b/tools/testing/selftests/rcutorture/configs/rcuscale/TINY
index c1a7d38823fb..f611b69f1189 100644
--- a/tools/testing/selftests/rcutorture/configs/rcuscale/TINY
+++ b/tools/testing/selftests/rcutorture/configs/rcuscale/TINY
@@ -11,7 +11,6 @@ CONFIG_NO_HZ_FULL=n
 CONFIG_RCU_NOCB_CPU=n
 CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_PROVE_LOCKING=n
-CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
 CONFIG_RCU_TRACE=y
diff --git a/tools/testing/selftests/rcutorture/configs/rcuscale/TRACE01 b/tools/testing/selftests/rcutorture/configs/rcuscale/TRACE01
index f3f1368b8386..69f5764159df 100644
--- a/tools/testing/selftests/rcutorture/configs/rcuscale/TRACE01
+++ b/tools/testing/selftests/rcutorture/configs/rcuscale/TRACE01
@@ -11,7 +11,6 @@ CONFIG_NO_HZ_FULL=n
 CONFIG_RCU_NOCB_CPU=n
 CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_PROVE_LOCKING=n
-CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
 CONFIG_RCU_TRACE=y
diff --git a/tools/testing/selftests/rcutorture/configs/rcuscale/TREE b/tools/testing/selftests/rcutorture/configs/rcuscale/TREE
index b10706fd03a4..5122cf08d5db 100644
--- a/tools/testing/selftests/rcutorture/configs/rcuscale/TREE
+++ b/tools/testing/selftests/rcutorture/configs/rcuscale/TREE
@@ -12,7 +12,6 @@ CONFIG_HIBERNATION=n
 CONFIG_RCU_NOCB_CPU=n
 CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_PROVE_LOCKING=n
-CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
 CONFIG_RCU_TRACE=y
diff --git a/tools/testing/selftests/rcutorture/configs/rcuscale/TREE54 b/tools/testing/selftests/rcutorture/configs/rcuscale/TREE54
index 9f83e5372796..08d30edb3b99 100644
--- a/tools/testing/selftests/rcutorture/configs/rcuscale/TREE54
+++ b/tools/testing/selftests/rcutorture/configs/rcuscale/TREE54
@@ -15,7 +15,6 @@ CONFIG_RCU_FANOUT_LEAF=2
 CONFIG_RCU_NOCB_CPU=n
 CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_PROVE_LOCKING=n
-CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
 CONFIG_RCU_TRACE=y
diff --git a/tools/testing/selftests/rcutorture/configs/refscale/NOPREEMPT b/tools/testing/selftests/rcutorture/configs/refscale/NOPREEMPT
index 1f215e17cbae..3e7d7793acc7 100644
--- a/tools/testing/selftests/rcutorture/configs/refscale/NOPREEMPT
+++ b/tools/testing/selftests/rcutorture/configs/refscale/NOPREEMPT
@@ -14,7 +14,6 @@ CONFIG_HIBERNATION=n
 CONFIG_RCU_NOCB_CPU=n
 CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_PROVE_LOCKING=n
-CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
 CONFIG_KPROBES=n
diff --git a/tools/testing/selftests/rcutorture/configs/refscale/PREEMPT b/tools/testing/selftests/rcutorture/configs/refscale/PREEMPT
index 52e3ef674056..feed29cf043f 100644
--- a/tools/testing/selftests/rcutorture/configs/refscale/PREEMPT
+++ b/tools/testing/selftests/rcutorture/configs/refscale/PREEMPT
@@ -12,6 +12,5 @@ CONFIG_HIBERNATION=n
 CONFIG_RCU_NOCB_CPU=n
 CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_PROVE_LOCKING=n
-CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
diff --git a/tools/testing/selftests/rcutorture/configs/refscale/TINY b/tools/testing/selftests/rcutorture/configs/refscale/TINY
index 9a11b578ff34..b67ea7a9128b 100644
--- a/tools/testing/selftests/rcutorture/configs/refscale/TINY
+++ b/tools/testing/selftests/rcutorture/configs/refscale/TINY
@@ -14,7 +14,6 @@ CONFIG_HIBERNATION=n
 CONFIG_RCU_NOCB_CPU=n
 CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_PROVE_LOCKING=n
-CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
 CONFIG_KPROBES=n
-- 
2.54.0


^ permalink raw reply related	[flat|nested] 2+ messages in thread

* Re: [PATCH for-v7.5 12/14] rcutorture: Enable RCU_BOOST where supported
  2026-11-13  0:57 ` [PATCH for-v7.5 12/14] rcutorture: Enable RCU_BOOST where supported Joel Fernandes
@ 2026-11-14  0:58   ` sashiko-bot
  0 siblings, 0 replies; 2+ messages in thread
From: sashiko-bot @ 2026-11-14  0:58 UTC (permalink / raw)
  To: Joel Fernandes; +Cc: linux-rt-devel, linux-kernel

Thank you for your contribution! Sashiko AI review found 3 potential
issues to consider:
- [Medium] rcutorture: promptless RCU_BOOST default y breaks
  BUSTED-BOOST negative test
- [Medium] rcutorture: unintended rcu_torture_boost() activation in
  NOCB01 and NOCB02
- [Low] rcu: Kconfig exposes RCU_BOOST_DELAY prompt when RCU_EXPERT=n
--

commit d21fbe9cdf60a4b081f0f993ea961ee602b93a2c
Author: Paul E. McKenney <paulmck@kernel.org>

rcutorture: Enable RCU_BOOST where supported

This commit drops the RCU_EXPERT dependency and prompt from RCU_BOOST so
that it is automatically enabled whenever RT_MUTEXES and PREEMPT_RCU
(or PREEMPT_RT) are enabled, and removes CONFIG_RCU_BOOST=n from
rcutorture config fragments.

> diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
> index bc9483c0b5d84..7b605fa1f576e 100644
> --- a/kernel/rcu/Kconfig
> +++ b/kernel/rcu/Kconfig
> @@ -237,17 +237,15 @@ config RCU_FANOUT_LEAF
>  	  Take the default if unsure.
>  
>  config RCU_BOOST
> -	bool "Enable RCU priority boosting"
> -	depends on (RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT) || PREEMPT_RT
> -	default y if PREEMPT_RT
> +	bool
> +	default y if (RT_MUTEXES && PREEMPT_RCU) || PREEMPT_RT

[Severity: Medium]
Does making RCU_BOOST a promptless symbol that defaults to y break the
BUSTED-BOOST rcutorture negative test added in d4240d628f98 ("rcutorture:
Add BUSTED-BOOST to test RCU priority boosting tests")?

BUSTED-BOOST sets CONFIG_PREEMPT=y (selecting CONFIG_PREEMPT_RCU=y) and
passes rcutorture.test_boost=2 so rcu_torture_can_boost() runs the boost
test on a kernel with CONFIG_RCU_BOOST=n to verify boost-failure
detection.  With this change, BUSTED-BOOST builds with CONFIG_RCU_BOOST=y
and cannot override it in its config fragment, so priority boosting is
active and the negative test passes instead of failing.

>  	help
>  	  This option boosts the priority of preempted RCU readers that
>  	  block the current preemptible RCU grace period for too long.
>  	  This option also prevents heavy loads from blocking RCU
> -	  callback invocation.
> +	  callback invocation.  It is now automatically enabled in
> +	  any kernel that can benefit from it and that can support it.
>  
> -	  Say Y here if you are working with real-time apps or heavy loads
> -	  Say N here if you are unsure.
>  
>  config RCU_BOOST_DELAY
>  	int "Milliseconds to delay boosting after RCU grace-period start"

[Severity: Low]
Will enabling RCU_BOOST when CONFIG_RCU_EXPERT=n expose the
RCU_BOOST_DELAY (and RCU_NOCB_CPU_CB_BOOST when NO_HZ_FULL selects
RCU_NOCB_CPU) prompts during make oldconfig on non-expert configurations?

Both options depend on RCU_BOOST and have unconditional prompts that were
previously hidden when RCU_EXPERT=n kept RCU_BOOST disabled.  Since
kernel/rcu/tree_plugin.h uses CONFIG_RCU_BOOST_DELAY unconditionally under
#ifdef CONFIG_RCU_BOOST, gating their prompts with "if RCU_EXPERT" would
keep the default value defined without prompting non-expert users.

> diff --git a/tools/testing/selftests/rcutorture/configs/rcu/NOCB01 b/tools/testing/selftests/rcutorture/configs/rcu/NOCB01
> index bbe6d28210ab5..91ca7e8b5725f 100644
> --- a/tools/testing/selftests/rcutorture/configs/rcu/NOCB01
> +++ b/tools/testing/selftests/rcutorture/configs/rcu/NOCB01
> @@ -14,7 +14,6 @@ CONFIG_RCU_FANOUT_LEAF=2
>  CONFIG_RCU_NOCB_CPU=y
>  CONFIG_DEBUG_LOCK_ALLOC=n
>  CONFIG_PROVE_LOCKING=n
> -CONFIG_RCU_BOOST=n
>  CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
>  CONFIG_RCU_EXPERT=y
>  CONFIG_RCU_EQS_DEBUG=y
> diff --git a/tools/testing/selftests/rcutorture/configs/rcu/NOCB02 b/tools/testing/selftests/rcutorture/configs/rcu/NOCB02
> index 4c2b8cd6d8fdb..ed3f3f7b29e73 100644
> --- a/tools/testing/selftests/rcutorture/configs/rcu/NOCB02
> +++ b/tools/testing/selftests/rcutorture/configs/rcu/NOCB02
> @@ -14,7 +14,6 @@ CONFIG_RCU_FANOUT_LEAF=2
>  CONFIG_RCU_NOCB_CPU=y
>  CONFIG_DEBUG_LOCK_ALLOC=n
>  CONFIG_PROVE_LOCKING=n
> -CONFIG_RCU_BOOST=n
>  CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
>  CONFIG_RCU_EXPERT=y
>  CONFIG_RCU_EQS_DEBUG=y

[Severity: Medium]
Does enabling CONFIG_RCU_BOOST=y in NOCB01 and NOCB02 unintentionally
start rcu_torture_boost() stress threads on these scenarios?

With CONFIG_RCU_TORTURE_TEST=y and CONFIG_RCU_BOOST=y,
sanitize_kthread_prio() raises kthread_prio to 2 and
rcu_torture_can_boost() returns true by default, spawning per-CPU
SCHED_FIFO rcu_torture_boost() threads on scenarios that leave rcuop
kthreads at SCHED_NORMAL without CONFIG_RCU_NOCB_CPU_CB_BOOST=y.  The
follow-up commit "rcutorture: Disable RCU priority boost testing on
non-TREE03 scenarios" adds rcutorture.test_boost=0 to TREE01, TREE02,
TREE08, and TREE09, but omits NOCB01.boot and NOCB02.boot.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261113005747.2977123-1-jfern@kernel.org?part=12

^ permalink raw reply	[flat|nested] 2+ messages in thread

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