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doc: Clarify RCU Tasks reader/updater checklist

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Currently, the reader/updater compatibility rules for the three RCU
Tasks flavors are squished together in a single paragraph, which can
result in confusion.  This commit therefore splits them out into a list,
clearly showing the distinction between these flavors.

Link: https://lore.kernel.org/all/20231002211936.5948253e@gandalf.local.home/

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.iitr10@gmail.com>
This commit is contained in:
Paul E. McKenney 2023-10-03 10:30:01 -07:00 committed by Neeraj Upadhyay (AMD)
parent 493dffa3ab
commit 1b7178b23d
1 changed files with 16 additions and 9 deletions
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25
Documentation/RCU/checklist.rst
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@ -241,15 +241,22 @@ over a rather long period of time, but improvements are always welcome!
srcu_struct. The rules for the expedited RCU grace-period-wait
primitives are the same as for their non-expedited counterparts.
If the updater uses call_rcu_tasks() or synchronize_rcu_tasks(),
then the readers must refrain from executing voluntary
context switches, that is, from blocking. If the updater uses
call_rcu_tasks_trace() or synchronize_rcu_tasks_trace(), then
the corresponding readers must use rcu_read_lock_trace() and
rcu_read_unlock_trace(). If an updater uses call_rcu_tasks_rude()
or synchronize_rcu_tasks_rude(), then the corresponding readers
must use anything that disables preemption, for example,
preempt_disable() and preempt_enable().
Similarly, it is necessary to correctly use the RCU Tasks flavors:
a. If the updater uses synchronize_rcu_tasks() or
call_rcu_tasks(), then the readers must refrain from
executing voluntary context switches, that is, from
blocking.
b. If the updater uses call_rcu_tasks_trace()
or synchronize_rcu_tasks_trace(), then the
corresponding readers must use rcu_read_lock_trace()
and rcu_read_unlock_trace().
c. If an updater uses call_rcu_tasks_rude() or
synchronize_rcu_tasks_rude(), then the corresponding
readers must use anything that disables preemption,
for example, preempt_disable() and preempt_enable().
Mixing things up will result in confusion and broken kernels, and
has even resulted in an exploitable security issue. Therefore,