This is a note to let you know that I've just added the patch titled
rcu: Make RCU_LOCKDEP_WARN() avoid early lockdep checks
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
rcu-make-rcu_lockdep_warn-avoid-early-lockdep-checks.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 029a55261f29f3e6e7ba211d231d4db212aeb6b8
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
Date: Wed Dec 14 11:41:44 2022 -0800
rcu: Make RCU_LOCKDEP_WARN() avoid early lockdep checks
[ 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@xxxxxxxxxxx>
Reported-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Reported-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 1e937a32da33d..13bddb841ceb1 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -313,11 +313,18 @@ static inline int rcu_read_lock_any_held(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); \
} \
