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 c0c79beac3fe6..8d4bf695e7666 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -376,11 +376,18 @@ 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); \ } \