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

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Date:   Tue,  2 Apr 2019 07:29:31 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     rcu@...r.kernel.org
Cc:     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,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        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: [PATCH RFC tip/core/rcu 2/4] drivers/gpu/drm: Dynamically allocate drm_unplug_srcu

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>
---
 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