Re: [PATCH 4/5] drm: Push drm_global_mutex locking in drm_open

Hi Daniel.

On Wed, Jan 29, 2020 at 09:24:09AM +0100, Daniel Vetter wrote:

We want to only take the BKL on crap drivers, but to know whether

The BKL was killed long time ago.. In other words I was confused until I realized that - BKL - drm_global_mutex BKL - drm_global_mutex

Was all the same. At least my OCD color me confused as is.

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.

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_globale_mutex locking (partially) opt-in like

s/drm_globale_mutex/drm_global_mutex/

with drm_release_noglobal().

Reviewed-by: Chris Wilson chris@chris-wilson.co.uk Cc: Chris Wilson chris@chris-wilson.co.uk Signed-off-by: Daniel Vetter daniel.vetter@intel.com

Above is IMO fix-while-committing stuff.

Sam

---

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 8deff75b484c..05bdf0b9d2b3 100644 --- a/drivers/gpu/drm/drm_drv.c +++ b/drivers/gpu/drm/drm_drv.c @@ -1085,17 +1085,14 @@ 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);

@@ -1104,10 +1101,9 @@ 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..d36cb74ebe0c 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_unlock(&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;

}

2.24.1

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