linux-kernel - [PATCH rcu v2 1/7] doc: Add broken-timing possibility to stallwarn.rst

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Message-Id: <20250130184925.1651665-1-paulmck@kernel.org>
Date: Thu, 30 Jan 2025 10:49:19 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	rostedt@...dmis.org,
	"Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu v2 1/7] doc: Add broken-timing possibility to stallwarn.rst

Currently, stallwarn.rst does not mention the fact that timer bugs can
result in false-positive RCU CPU stall warnings.  This commit therefore
adds this to the list.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 Documentation/RCU/stallwarn.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/RCU/stallwarn.rst b/Documentation/RCU/stallwarn.rst
index 30080ff6f406..d1ccd6039a8c 100644
--- a/Documentation/RCU/stallwarn.rst
+++ b/Documentation/RCU/stallwarn.rst
@@ -96,6 +96,13 @@ warnings:
 	the ``rcu_.*timer wakeup didn't happen for`` console-log message,
 	which will include additional debugging information.
 
+-	A timer issue causes time to appear to jump forward, so that RCU
+	believes that the RCU CPU stall-warning timeout has been exceeded
+	when in fact much less time has passed.  This could be due to
+	timer hardware bugs, timer driver bugs, or even corruption of
+	the "jiffies" global variable.	These sorts of timer hardware
+	and driver bugs are not uncommon when testing new hardware.
+
 -	A low-level kernel issue that either fails to invoke one of the
 	variants of rcu_eqs_enter(true), rcu_eqs_exit(true), ct_idle_enter(),
 	ct_idle_exit(), ct_irq_enter(), or ct_irq_exit() on the one
-- 
2.40.1