Re: [PATCH rcu 3/5] doc: Clarify RCU Tasks reader/updater checklist

[Joel Fernandes]

> On Dec 12, 2023, at 12:27 PM, Neeraj Upadhyay (AMD) <neeraj.iitr10@xxxxxxxxx> wrote:
> 
> From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> 
> 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@xxxxxxxxxxxxxxxxxx/
> 
> Reported-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> Reviewed-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.iitr10@xxxxxxxxx>
> ---
> Documentation/RCU/checklist.rst | 25 ++++++++++++++++---------
> 1 file changed, 16 insertions(+), 9 deletions(-)
> 
> diff --git a/Documentation/RCU/checklist.rst b/Documentation/RCU/checklist.rst
> index bd3c58c44bef..c432899aff22 100644
> --- a/Documentation/RCU/checklist.rst
> +++ b/Documentation/RCU/checklist.rst
> @@ -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 necssary to correctly use the RCU Tasks flavors:

Typo: necessary.

Probably no need to resend this one, just fix in the PR.

Thanks,

 - Joel




> +
> +    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,
> -- 
> 2.40.1
> 
>