Commit 591a2abf authored Feb 04, 2020 by Daniel Vetter

drm: Push drm_global_mutex locking in drm_open



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

parent c368ec19

drivers/gpu/drm/drm_drv.c

+5 −9

Original line number	Diff line number	Diff line
		@@ -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;
		}

drivers/gpu/drm/drm_file.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -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;
		}

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