leandrof/linux
1
0
Fork 0
forked from Minki/linux
Code Issues Pull Requests Packages Projects Releases Wiki Activity

drm: Drop grab fpriv->fbs_lock in drm_fb_release

Browse Source 
Paulo Zanoni reported a lockdep splat with a locking inversion between
fpriv->fbs_lock and the modeset locks. This issue was introduced in

commit f2b50c1161
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Fri Sep 12 17:07:32 2014 +0200

    drm: Fixup locking for universal cursor planes

This here is actually one of the rare cases where lockdep hits a false
positive: The deadlock only happens in drm_fb_release, which cleans up
the file private structure when all the references are gone. So the
locking is the very last one and no one else can deadlock. It also
doesn't protect anything at all, since all ioctls are guaranteed to
have returned at this point - otherwise they'd still hold a reference
on the file.

So let's just drop it and replace it with a big comment.

Cc: David Herrmann <dh.herrmann@gmail.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Paulo Zanoni <przanoni@gmail.com>
Reported-and-Tested-by: Paulo Zanoni <przanoni@gmail.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
This commit is contained in:
Daniel Vetter 2014-09-24 21:51:06 +02:00
parent ee0d68ab5f
commit 1b11629737
1 changed files with 10 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
drivers/gpu/drm/drm_crtc.c
View File

@ -3400,7 +3400,16 @@ void drm_fb_release(struct drm_file *priv)
struct drm_device *dev = priv->minor->dev;
struct drm_framebuffer *fb, *tfb;
mutex_lock(&priv->fbs_lock);
/*
* When the file gets released that means no one else can access the fb
* list any more, so no need to grab fpriv->fbs_lock. And we need to to
* avoid upsetting lockdep since the universal cursor code adds a
* framebuffer while holding mutex locks.
*
* Note that a real deadlock between fpriv->fbs_lock and the modeset
* locks is impossible here since no one else but this function can get
* at it any more.
*/
list_for_each_entry_safe(fb, tfb, &priv->fbs, filp_head) {
mutex_lock(&dev->mode_config.fb_lock);
@ -3413,7 +3422,6 @@ void drm_fb_release(struct drm_file *priv)
/* This will also drop the fpriv->fbs reference. */
drm_framebuffer_remove(fb);
}
mutex_unlock(&priv->fbs_lock);
}
/**