[PATCH AUTOSEL 6.2 04/53] rcu: Make RCU_LOCKDEP_WARN() avoid early lockdep checks

Sasha Levin
2023-02-26T14:45:07Z

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

[ Upstream commit 0cae5ded535c3a80aed94f119bbd4ee3ae284a65 ]

Currently, RCU_LOCKDEP_WARN() checks the condition before checking
to see if lockdep is still enabled. This is necessary to avoid the
false-positive splats fixed by commit 3066820034b5dd ("rcu: Reject
RCU_LOCKDEP_WARN() false positives"). However, the current state can
result in false-positive splats during early boot before lockdep is fully
initialized. This commit therefore checks debug_lockdep_rcu_enabled()
both before and after checking the condition, thus avoiding both sets
of false-positive error reports.

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Reported-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/rcupdate.h | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 03abf883a281b..aa86de01aab6d 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -374,11 +374,18 @@ static inline int debug_lockdep_rcu_enabled(void)
* RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
* @c: condition to check
* @s: informative message
+ *
+ * This checks debug_lockdep_rcu_enabled() before checking (c) to
+ * prevent early boot splats due to lockdep not yet being initialized,
+ * and rechecks it after checking (c) to prevent false-positive splats
+ * due to races with lockdep being disabled. See commit 3066820034b5dd
+ * ("rcu: Reject RCU_LOCKDEP_WARN() false positives") for more detail.
*/
#define RCU_LOCKDEP_WARN(c, s) \
do { \
static bool __section(".data.unlikely") __warned; \
- if ((c) && debug_lockdep_rcu_enabled() && !__warned) { \
+ if (debug_lockdep_rcu_enabled() && (c) && \
+ debug_lockdep_rcu_enabled() && !__warned) { \
__warned = true; \
lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
} \
--
2.39.0