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From:   Joel Fernandes <joel@joelfernandes.org>
Mime-Version: 1.0 (1.0)
Subject: Re: [PATCH rcu 3/5] doc: Clarify RCU Tasks reader/updater checklist
Date:   Tue, 12 Dec 2023 15:09:28 -0500
Message-Id: <019C4075-EDA3-48A9-8762-CBB28D0BA37C@joelfernandes.org>
References: <20231212172653.11485-3-neeraj.iitr10@gmail.com>
Cc:     rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@meta.com, rostedt@goodmis.org, paulmck@kernel.org,
        Neeraj.Upadhyay@amd.com,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
In-Reply-To: <20231212172653.11485-3-neeraj.iitr10@gmail.com>
To:     "Neeraj Upadhyay (AMD)" <neeraj.iitr10@gmail.com>
Precedence: bulk


> On Dec 12, 2023, at 12:27 PM, Neeraj Upadhyay (AMD) <neeraj.iitr10@gmail.c=
om> wrote:
>=20
> =EF=BB=BFFrom: "Paul E. McKenney" <paulmck@kernel.org>
>=20
> 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.
>=20
> Link: https://lore.kernel.org/all/20231002211936.5948253e@gandalf.local.ho=
me/
>=20
> 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>
> ---
> Documentation/RCU/checklist.rst | 25 ++++++++++++++++---------
> 1 file changed, 16 insertions(+), 9 deletions(-)
>=20
> 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 a=
re always welcome!
>    srcu_struct.  The rules for the expedited RCU grace-period-wait
>    primitives are the same as for their non-expedited counterparts.
>=20
> -    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().
>=20
>    Mixing things up will result in confusion and broken kernels, and
>    has even resulted in an exploitable security issue.  Therefore,
> --=20
> 2.40.1
>=20
>=20