panic: sleeping without a mutex (acd related)

I have been experiencing some random lockups after upgrading from
5.1-RELEASE to 5.2-BETA.

I then wen on and enabled all the debug options in my kernel config
hoping to be able to find the cause.

But now I cannot boot at all. In the end of the boot process when
detecting ATA drives, I get this:

ad0: 76319MB <ST380011A> [155061/16/63] at ata0-master UDMA100                  
acd0-5: CDROM with 6 CD changer <CD-C68E> at ata1-master PIO4                   
acd6: DVDROM <CREATIVEDVD5240E-1> at ata1-slave PIO4                            
panic: sleeping without a mutex                                                 
Debugger("panic")                                                               
Stopped at      Debugger+0x54:  xchgl   %ebx,in_Debugger.0                      
db>                                                                             
db> trace                                                                       
Debugger(c06e3744,c07549a0,c06e3ec9,d861ab60,100) at Debugger+0x54              
panic(c06e3ec9,0,c06e3eb8,c06d6584,10) at panic+0xd5                            
msleep(c45173d8,0,4c,c06d6584,0) at msleep+0x505                                
acd_geom_access(c452de00,1,0,0,0) at acd_geom_access+0x115                      
g_access_rel(c4509280,1,0,0,d861aca0) at g_access_rel+0x20d                     
g_slice_new(c0742a60,4,c452de00,d861ac9c,d861aca0) at g_slice_new+0xea          
g_mbr_taste(c0742a60,c452de00,0,15b,c452dd80) at g_mbr_taste+0x90               
g_new_provider_event(c452de00,0,c06de186,b5,66666667) at g_new_provider_event+0d
one_event(d861ad10,c04f2b95,c074f994,0,4c) at one_event+0x218                   
g_run_events(c074f994,0,4c,c06dd10e,a) at g_run_events+0x15                     
g_event_procbody(0,d861ad48,c06e1304,311,2cb966) at g_event_procbody+0x45       
fork_exit(c04f2b50,0,d861ad48) at fork_exit+0xb4                                
fork_trampoline() at fork_trampoline+0x8                                        
--- trap 0x1, eip = 0, esp = 0xd861ad7c, ebp = 0 ---                            

I am not a kernel expert but the problem seems to be related to acd.

-- 
Best regards
    Christian Laursen