Patch "rcu: Make RCU_LOCKDEP_WARN() avoid early lockdep checks" has been added to the 5.10-stable tree

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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 5.10-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-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 05f0ec39fcfbbff84d5adf498c64de45da8c680b
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 1f46db38d6ec6..ef8d56b18da6b 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -308,11 +308,18 @@ 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);	\
 		}							\



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