From a4b6b041148448c99f73033ecaa9ae7e611252ba Mon Sep 17 00:00:00 2001
From: Daniel Vetter <daniel.vetter@ffwll.ch>
Date: Tue, 4 Feb 2020 16:01:45 +0100
Subject: drm: Push drm_global_mutex locking in drm_open
Git-commit: 591a2abf149f6fa14807992eca60c9ee359f114d
Patch-mainline: v5.7-rc1
References: jsc#SLE-12680, jsc#SLE-12880, jsc#SLE-12882, jsc#SLE-12883, jsc#SLE-13496, jsc#SLE-15322

We want to only take the BKL on crap drivers, but to know whether
we have a crap driver we first need to look it up. Split this shuffle
out from the main BKL-disabling patch, for more clarity. Historical
aside: When the kernel-wide BKL was removed, it was replaced by
drm_global_mutex within the scope of the drm subsystem hence why these
two things are (almost) interchangeable as concepts here.

Since the minors are refcounted drm_minor_acquire is purely internal
and this does not have a driver visible effect.

v2: Push the locking even further into drm_open(), suggested by Chris.
This gives us more symmetry with drm_release(), and maybe a futuer
avenue where we make drm_global_mutex locking (partially) opt-in like
with drm_release_noglobal().

v3:
- Actually push this stuff correctly, don't unlock twice (Chris)
- Fix typo on commit message, plus explain why BKL = drm_global_mutex
  (Sam)

Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200204150146.2006481-5-daniel.vetter@ffwll.ch
Signed-off-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 drivers/gpu/drm/drm_drv.c  | 14 +++++---------
 drivers/gpu/drm/drm_file.c |  6 ++++++
 2 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 7c18a980cd4b..b8f716e61037 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -1079,17 +1079,14 @@ static int drm_stub_open(struct inode *inode, struct file *filp)
 
 	DRM_DEBUG("\n");
 
-	mutex_lock(&drm_global_mutex);
 	minor = drm_minor_acquire(iminor(inode));
-	if (IS_ERR(minor)) {
-		err = PTR_ERR(minor);
-		goto out_unlock;
-	}
+	if (IS_ERR(minor))
+		return PTR_ERR(minor);
 
 	new_fops = fops_get(minor->dev->driver->fops);
 	if (!new_fops) {
 		err = -ENODEV;
-		goto out_release;
+		goto out;
 	}
 
 	replace_fops(filp, new_fops);
@@ -1098,10 +1095,9 @@ static int drm_stub_open(struct inode *inode, struct file *filp)
 	else
 		err = 0;
 
-out_release:
+out:
 	drm_minor_release(minor);
-out_unlock:
-	mutex_unlock(&drm_global_mutex);
+
 	return err;
 }
 
diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
index 1075b3a8b5b1..80d556402ab4 100644
--- a/drivers/gpu/drm/drm_file.c
+++ b/drivers/gpu/drm/drm_file.c
@@ -378,6 +378,8 @@ int drm_open(struct inode *inode, struct file *filp)
 	if (IS_ERR(minor))
 		return PTR_ERR(minor);
 
+	mutex_lock(&drm_global_mutex);
+
 	dev = minor->dev;
 	if (!atomic_fetch_inc(&dev->open_count))
 		need_setup = 1;
@@ -395,10 +397,14 @@ int drm_open(struct inode *inode, struct file *filp)
 			goto err_undo;
 		}
 	}
+
+	mutex_unlock(&drm_global_mutex);
+
 	return 0;
 
 err_undo:
 	atomic_dec(&dev->open_count);
+	mutex_unlock(&drm_global_mutex);
 	drm_minor_release(minor);
 	return retcode;
 }
-- 
2.28.0