linux-kernel - Re: [PATCH RFC tip/core/rcu 0/4] Forbid static SRCU use in modules

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Message-ID: <886051277.1395.1554218080591.JavaMail.zimbra@efficios.com>
Date:   Tue, 2 Apr 2019 11:14:40 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     paulmck <paulmck@...ux.ibm.com>
Cc:     rcu@...r.kernel.org, linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        dipankar <dipankar@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josh Triplett <josh@...htriplett.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        rostedt <rostedt@...dmis.org>,
        David Howells <dhowells@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        fweisbec <fweisbec@...il.com>, Oleg Nesterov <oleg@...hat.com>,
        "Joel Fernandes, Google" <joel@...lfernandes.org>,
        linux-nvdimm@...ts.01.org, dri-devel@...ts.freedesktop.org,
        amd-gfx@...ts.freedesktop.org
Subject: Re: [PATCH RFC tip/core/rcu 0/4] Forbid static SRCU use in modules

----- On Apr 2, 2019, at 10:28 AM, paulmck paulmck@...ux.ibm.com wrote:

> Hello!
> 
> This series prohibits use of DEFINE_SRCU() and DEFINE_STATIC_SRCU()
> by loadable modules.  The reason for this prohibition is the fact
> that using these two macros within modules requires that the size of
> the reserved region be increased, which is not something we want to
> be doing all that often.  Instead, loadable modules should define an
> srcu_struct and invoke init_srcu_struct() from their module_init function
> and cleanup_srcu_struct() from their module_exit function.  Note that
> modules using call_srcu() will also need to invoke srcu_barrier() from
> their module_exit function.

This arbitrary API limitation seems weird.

Isn't there a way to allow modules to use DEFINE_SRCU and DEFINE_STATIC_SRCU
while implementing them with dynamic allocation under the hood ?

Thanks,

Mathieu


> 
> This series consist of the following:
> 
> 1.	Dynamically allocate dax_srcu.
> 
> 2.	Dynamically allocate drm_unplug_srcu.
> 
> 3.	Dynamically allocate kfd_processes_srcu.
> 
> These build and have been subjected to 0day testing, but might also need
> testing by someone having the requisite hardware.
> 
>							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> drivers/dax/super.c                        |   10 +++++-
> drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd.c |    5 +++
> drivers/gpu/drm/amd/amdkfd/kfd_process.c   |    2 -
> drivers/gpu/drm/drm_drv.c                  |    8 ++++
> include/linux/srcutree.h                   |   19 +++++++++--
> kernel/rcu/rcuperf.c                       |   40 +++++++++++++++++++-----
> kernel/rcu/rcutorture.c                    |   48 +++++++++++++++++++++--------
>  7 files changed, 105 insertions(+), 27 deletions(-)

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com