linux-kernel - [PATCH tip/core/rcu 05/18] Default enable RCU list lockdep debugging with PROVE

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Message-Id: <20200415173100.9927-5-paulmck@kernel.org>
Date:   Wed, 15 Apr 2020 10:30:47 -0700
From:   paulmck@...nel.org
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>,
        Amol Grover <frextrite@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH tip/core/rcu 05/18] Default enable RCU list lockdep debugging with PROVE_RCU

From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>

This patch default enables CONFIG_PROVE_RCU_LIST option with
CONFIG_PROVE_RCU for RCU list lockdep debugging.

With this change, RCU list lockdep debugging will be default
enabled in CONFIG_PROVE_RCU=y kernels.

Most of the RCU users (in core kernel/, drivers/, and net/
subsystem) have already been modified to include lockdep
expressions hence RCU list debugging can be enabled by
default.

However, there are still chances of enountering
false-positive lockdep splats because not everything is converted,
in case RCU list primitives are used in non-RCU read-side critical
section but under the protection of a lock. It would be okay to
have a few false-positives, as long as bugs are identified, since this
patch only affects debugging kernels.

Co-developed-by: Amol Grover <frextrite@...il.com>
Signed-off-by: Amol Grover <frextrite@...il.com>
Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
Acked-by: Joel Fernandes (Google) <joel@...lfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/Kconfig.debug | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 4aa02ee..ec4bb6c 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -9,15 +9,10 @@ config PROVE_RCU
 	def_bool PROVE_LOCKING
 
 config PROVE_RCU_LIST
-	bool "RCU list lockdep debugging"
-	depends on PROVE_RCU && RCU_EXPERT
-	default n
+	def_bool PROVE_RCU
 	help
-	  Enable RCU lockdep checking for list usages. By default it is
-	  turned off since there are several list RCU users that still
-	  need to be converted to pass a lockdep expression. To prevent
-	  false-positive splats, we keep it default disabled but once all
-	  users are converted, we can remove this config option.
+	  Enable RCU lockdep checking for list usages. It is default
+	  enabled with CONFIG_PROVE_RCU.
 
 config TORTURE_TEST
 	tristate
-- 
2.9.5