linux-kernel - Re: [PATCH v4] uapi/linux/prctl: provide macro definitions for the PR_SCHED

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Message-ID: <20210826100025.pdakvmg24gomnuk5@wittgenstein>
Date:   Thu, 26 Aug 2021 12:00:25 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Eugene Syromiatnikov <esyr@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Chris Hyser <chris.hyser@...cle.com>,
        Josh Don <joshdon@...gle.com>, Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "Dmitry V. Levin" <ldv@...ace.io>, linux-doc@...r.kernel.org,
        linux-api@...r.kernel.org, Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH v4] uapi/linux/prctl: provide macro definitions for the
 PR_SCHED_CORE type argument

On Wed, Aug 25, 2021 at 07:06:13PM +0200, Eugene Syromiatnikov wrote:
> Commit 7ac592aa35a684ff ("sched: prctl() core-scheduling interface")
> made use of enum pid_type in prctl's arg4; this type and the associated
> enumeration definitions are not exposed to userspace.  Christian
> has suggested to provide additional macro definitions that convey
> the meaning of the type argument more in alignment with its actual
> usage, and this patch does exactly that.
> 
> Suggested-by: Christian Brauner <christian.brauner@...ntu.com>
> Complements: 7ac592aa35a684ff ("sched: prctl() core-scheduling interface")
> Signed-off-by: Eugene Syromiatnikov <esyr@...hat.com>
> ---

I mean, I proposed the names so I'm ok with them. :)
Acked-by: Christian Brauner <christian.brauner@...ntu.com>

Peter et al. are you ok with this and do the names make sense to you?

Christian

> v4:
>   - Rewritten in accordance with Christian Brauner's suggestion to provide
>     macro definitions that are explicitly tailored for the prctl op.
> 
> v3: https://lore.kernel.org/lkml/20210807120905.GA14706@asgard.redhat.com/
>   - Fixed header guard macro: s/_UAPI_LINUX_PID_H/_UAPI_LINUX_PIDTYPE_H/,
>     as noted by Dmitry Levin.
> 
> v2: https://lore.kernel.org/lkml/20210807104800.GA22620@asgard.redhat.com/
>   - Header file is renamed from pid.h to pidtype.h to avoid collisions
>     with include/linux/pid.h when included from uapi headers;
>   - The enum type has renamed from __kernel_pid_type to __kernel_pidtype
>     to avoid possible confusion with __kernel_pid_t.
> 
> v1: https://lore.kernel.org/lkml/20210807010123.GA5174@asgard.redhat.com/
> ---
>  Documentation/admin-guide/hw-vuln/core-scheduling.rst | 5 +++--
>  include/uapi/linux/prctl.h                            | 3 +++
>  kernel/sched/core_sched.c                             | 4 ++++
>  3 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/admin-guide/hw-vuln/core-scheduling.rst b/Documentation/admin-guide/hw-vuln/core-scheduling.rst
> index 7b410ae..9a65fed 100644
> --- a/Documentation/admin-guide/hw-vuln/core-scheduling.rst
> +++ b/Documentation/admin-guide/hw-vuln/core-scheduling.rst
> @@ -61,8 +61,9 @@ arg3:
>      ``pid`` of the task for which the operation applies.
>  
>  arg4:
> -    ``pid_type`` for which the operation applies. It is of type ``enum pid_type``.
> -    For example, if arg4 is ``PIDTYPE_TGID``, then the operation of this command
> +    ``pid_type`` for which the operation applies. It is one of
> +    ``PR_SCHED_CORE_SCOPE_``-prefixed macro constants.  For example, if arg4
> +    is ``PR_SCHED_CORE_SCOPE_THREAD_GROUP``, then the operation of this command
>      will be performed for all tasks in the task group of ``pid``.
>  
>  arg5:
> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> index 967d9c5..644a3b4 100644
> --- a/include/uapi/linux/prctl.h
> +++ b/include/uapi/linux/prctl.h
> @@ -266,5 +266,8 @@ struct prctl_mm_map {
>  # define PR_SCHED_CORE_SHARE_TO		2 /* push core_sched cookie to pid */
>  # define PR_SCHED_CORE_SHARE_FROM	3 /* pull core_sched cookie to pid */
>  # define PR_SCHED_CORE_MAX		4
> +# define PR_SCHED_CORE_SCOPE_THREAD		0
> +# define PR_SCHED_CORE_SCOPE_THREAD_GROUP	1
> +# define PR_SCHED_CORE_SCOPE_PROCESS_GROUP	2
>  
>  #endif /* _LINUX_PRCTL_H */
> diff --git a/kernel/sched/core_sched.c b/kernel/sched/core_sched.c
> index 9a80e9a..20f6409 100644
> --- a/kernel/sched/core_sched.c
> +++ b/kernel/sched/core_sched.c
> @@ -134,6 +134,10 @@ int sched_core_share_pid(unsigned int cmd, pid_t pid, enum pid_type type,
>  	if (!static_branch_likely(&sched_smt_present))
>  		return -ENODEV;
>  
> +	BUILD_BUG_ON(PR_SCHED_CORE_SCOPE_THREAD != PIDTYPE_PID);
> +	BUILD_BUG_ON(PR_SCHED_CORE_SCOPE_THREAD_GROUP != PIDTYPE_TGID);
> +	BUILD_BUG_ON(PR_SCHED_CORE_SCOPE_PROCESS_GROUP != PIDTYPE_PGID);
> +
>  	if (type > PIDTYPE_PGID || cmd >= PR_SCHED_CORE_MAX || pid < 0 ||
>  	    (cmd != PR_SCHED_CORE_GET && uaddr))
>  		return -EINVAL;
> -- 
> 2.1.4
>