Commit 0cae5ded authored Dec 14, 2022 by Paul E. McKenney

rcu: Make RCU_LOCKDEP_WARN() avoid early lockdep checks



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 30668200 ("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>

parent 95ff24ee

include/linux/rcupdate.h

+8 −1

Original line number	Diff line number	Diff line
		@@ -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); \
		} \