linux-kernel - [RFC lockdep 3/4] rcu/lockdep: Annotate the rcu_callback

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Date:   Tue,  8 Dec 2020 18:31:11 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     linux-kernel@...r.kernel.org, rcu@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Boqun Feng <boqun.feng@...il.com>
Subject: [RFC lockdep 3/4] rcu/lockdep: Annotate the rcu_callback_map with proper wait contexts

rcu_callback_map is a virtual lock to annotate a context where RCU
callbacks are executed. RCU callbacks are required in softirq disable
contexts because with some config combination (use_softirq is true and
nocb is disabled) RCU callbacks only execute in softirq contexts.
Therefore wait context annotations can be added to detect bugs like
using mutex in a RCU callback.

Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
 kernel/rcu/update.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 39334d2d2b37..dd59e6412f61 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -269,8 +269,12 @@ EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
 
 // Tell lockdep when RCU callbacks are being invoked.
 static struct lock_class_key rcu_callback_key;
-struct lockdep_map rcu_callback_map =
-	STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key);
+struct lockdep_map rcu_callback_map = {
+	.name = "rcu_callback",
+	.key = &rcu_callback_key,
+	.wait_type_outer = LD_WAIT_FREE,
+	.wait_type_inner = LD_WAIT_CONFIG, /* RCU callbacks are handled in softirq context */
+};
 EXPORT_SYMBOL_GPL(rcu_callback_map);
 
 noinstr int notrace debug_lockdep_rcu_enabled(void)
-- 
2.29.2