linux-kernel - Re: [PATCH RFC tip/core/rcu 2/4] drivers/gpu/drm: Dynamically allocate drm_unplug

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Date:   Tue, 2 Apr 2019 18:14:28 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Tejun Heo <tj@...nel.org>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH RFC tip/core/rcu 2/4] drivers/gpu/drm: Dynamically
 allocate drm_unplug_srcu

On Tue, Apr 02, 2019 at 07:29:31AM -0700, Paul E. McKenney wrote:
> Having DEFINE_SRCU() or DEFINE_STATIC_SRCU() in a loadable module
> requires that the size of the reserved region be increased, which is not
> something we really want to be doing.  This commit therefore removes
> the DEFINE_STATIC_SRCU() from drivers/gpu/drm/drm_drv.c in favor of
> defining drm_unplug_srcu as a simple srcu_struct, initializing it in
> drm_core_init(), and cleaning it up in drm_core_exit().
> 
> In this particular case, drm_unplug_srcu is statically allocated and thus
> guaranteed to be initially zero.  Unfortunately, cleanup_srcu_struct()
> cannot rely on this in the general case (which includes dynamically
> allocated srcu_struct structures), and therefore cannot tell whether it
> is being called on something that has been passed to init_srcu_struct().
> Thus the code added to drm_core_init() is a bit non-standard.
> 
> Reported-by: kbuild test robot <lkp@...el.com>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
> Cc: Maxime Ripard <maxime.ripard@...tlin.com>
> Cc: Sean Paul <sean@...rly.run>
> Cc: David Airlie <airlied@...ux.ie>
> Cc: Daniel Vetter <daniel@...ll.ch>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: <dri-devel@...ts.freedesktop.org>

Seems reasonable (but I don't have the full patch series as context).

Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>

Any preferences as to how this should be merged? Upfront ack for merging
through rcu trees if that helps you.
-Daniel
> ---
>  drivers/gpu/drm/drm_drv.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index 381581b01d48..ce4582af814d 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -77,7 +77,7 @@ static bool drm_core_init_complete = false;
>  
>  static struct dentry *drm_debugfs_root;
>  
> -DEFINE_STATIC_SRCU(drm_unplug_srcu);
> +static struct srcu_struct drm_unplug_srcu;
>  
>  /*
>   * DRM Minors
> @@ -958,12 +958,18 @@ static void drm_core_exit(void)
>  	drm_sysfs_destroy();
>  	idr_destroy(&drm_minors_idr);
>  	drm_connector_ida_destroy();
> +	cleanup_srcu_struct(&drm_unplug_srcu);
>  }
>  
>  static int __init drm_core_init(void)
>  {
>  	int ret;
>  
> +	ret = init_srcu_struct(&drm_unplug_srcu);
> +	if (ret) {
> +		DRM_ERROR("Cannot create DRM class: %d\n", ret);
> +		return ret; /* cannot cleanup after failed srcu_struct init. */
> +	}
>  	drm_connector_ida_init();
>  	idr_init(&drm_minors_idr);
>  
> -- 
> 2.17.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch