re: port-i386/53364: System crashes soon after X server is started with viadrm driver

[matthew green <mrg%eterna.com.au@localhost>]

The following reply was made to PR port-i386/53364; it has been noted by GNATS.

From: matthew green <mrg%eterna.com.au@localhost>
To: Andrius V <vezhlys%gmail.com@localhost>
Cc: gnats-bugs%netbsd.org@localhost, port-i386-maintainer%netbsd.org@localhost,
    gnats-admin%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost
Subject: re: port-i386/53364: System crashes soon after X server is started with viadrm driver
Date: Mon, 18 Jun 2018 12:21:31 +1000

 > #7  0xc085141b in mutex_oncpu (owner=4294967280) at
 > ../../../../kern/kern_mutex.c:551
 
 i see why the fault occurs:
 
 here owner = 0xfffffff0.  that seems bogus because it should
 be a pointer.  and l_cpu is offset 12 in struct lwp:
 
     413 mutex_oncpu(uintptr_t owner)
     [ ... ]
     416         lwp_t *l;
     [ ... ]
     428         l = (lwp_t *)MUTEX_OWNER(owner);
     429         ci = l->l_cpu;
 
 so that explains the 0xfffffffc fault address.
 
 the real question is why is this invalid.  it should be valid.
 
 > #8  mutex_vector_enter (mtx=0xc370edc4) at ../../../../kern/kern_mutex.c:560
 > #9  0xc0722bee in via_dmablit_grab_slot (engine=1, blitq=0xc370ed78)
 > at ../../../../external/bsd/drm/dist/bsd-core/via_dmablit.c:670
 > #10 via_dmablit (xfer=0xdc161eac, dev=0xc3652400) at
 > ../../../../external/bsd/drm/dist/bsd-core/via_dmablit.c:723
 [ ... ]
 > (gdb) print blitq->dev
 > $26 = (struct drm_device *) 0xc3652400
 > (gdb) print blitq->cur_blit_handle
 > $27 = 0
 > (gdb) print blitq->done_blit_handle
 
 BTW, you could probably use "print *blitq" here, to view the whole
 structure.  if you "set print pretty" first, it will be readable ;)
 
 > Is there anything more I can provide? Thank you.
 
 at this point, i suspect that we have a locking issue and the
 first step here is normally to build a kernel with LOCKDEBUG
 enabled and see what happens.  it hopefully will crash earlier
 and with more information about what is wrong.
 
 thanks!
 
 
 .mrg.