Hi Dri devs,

Witold Baryluk baryluk@smp.if.uj.edu.pl reported a lockdep splat to the fbdev list, but apparently that was the wrong list and you people are the right list to handle this.

Here is the lockdep splat and Witold's config: http://marc.info/?l=linux-fbdev&m=133883191129462&w=2

I looked into the bug and it turns out there is a lock ordering problem but I'm not sure how to fix it. http://marc.info/?l=linux-fbdev&m=133890563322819&w=2

Cut and pasted from that URL: ----------- The problem is we hold ->mmap_sem when we call fb_release() which takes the info->lock.

We take the info->lock in do_fb_ioctl() before we call fb_set_var() which calls drm_fb_helper_set_par() which takes the mode_config.mutex.

In drm_mode_getresources() we take the mode_config.mutex() and call put_user() which takes the ->mmap_sem.

So on one CPU we are holding the ->mmap_sem and want the info->lock. On another CPU we are holding the info->lock and want the config.mutex. On the other CPU we hold the config.mutex and want the ->mmap_sem.

Deadlock. -----------

Could you take a look?

regards, dan carpenter