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doc: Add another stall-warning root cause in stallwarn.rst

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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@kernel.org>
This commit is contained in:
Paul E. McKenney 2021-07-22 21:41:48 -07:00
parent 9424b867a7
commit 13bc8fa805
1 changed files with 10 additions and 0 deletions
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10
Documentation/RCU/stallwarn.rst
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@ -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