This commit adds a bullet item noting that both deficiencies and surpluses of calls to rcu_*_enter() and rcu_*_exit() can result in RCU CPU stall warnings. Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> --- Documentation/RCU/stallwarn.rst | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/Documentation/RCU/stallwarn.rst b/Documentation/RCU/stallwarn.rst index 5036df24ae61..28f8ad16db25 100644 --- a/Documentation/RCU/stallwarn.rst +++ b/Documentation/RCU/stallwarn.rst @@ -96,6 +96,16 @@ warnings: the ``rcu_.*timer wakeup didn't happen for`` console-log message, which will include additional debugging information. +- A low-level kernel issue that either fails to invoke one of the + variants of rcu_user_enter(), rcu_user_exit(), rcu_idle_enter(), + rcu_idle_exit(), rcu_irq_enter(), or rcu_irq_exit() on the one + hand, or that invokes one of them too many times on the other. + Historically, the most frequent issue has been an omission + of either irq_enter() or irq_exit(), which in turn invoke + rcu_irq_enter() or rcu_irq_exit(), respectively. Building your + kernel with CONFIG_RCU_EQS_DEBUG=y can help track down these types + of issues, which sometimes arise in architecture-specific code. + - A bug in the RCU implementation. - A hardware failure. This is quite unlikely, but has occurred -- 2.31.1.189.g2e36527f23
