[PATCH RFC tip/core/rcu 2/4] drivers/gpu/drm: Dynamically allocate drm_unplug_srcu

From: Paul E. McKenney
Date: Tue Apr 02 2019 - 10:30:34 EST

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@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Maxime Ripard <maxime.ripard@xxxxxxxxxxx>
Cc: Sean Paul <sean@xxxxxxxxxx>
Cc: David Airlie <airlied@xxxxxxxx>
Cc: Daniel Vetter <daniel@xxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: <dri-devel@xxxxxxxxxxxxxxxxxxxxx>
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;

+static struct srcu_struct drm_unplug_srcu;

* DRM Minors
@@ -958,12 +958,18 @@ static void drm_core_exit(void)
+ 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. */
+ }