On Mon, Apr 6, 2020 at 3:34 PM Lyude Paul lyude@redhat.com wrote:

While we don't need this function to store an mstb anywhere for UP requests since we process them asynchronously, we do need to make sure that we don't try to write to **mstb for UP requests otherwise we'll cause a NULL pointer deref:

RIP: 0010:drm_dp_get_one_sb_msg+0x4b/0x460 [drm_kms_helper]
Call Trace:
 ? vprintk_emit+0x16a/0x230
 ? drm_dp_mst_hpd_irq+0x133/0x1010 [drm_kms_helper]
 drm_dp_mst_hpd_irq+0x133/0x1010 [drm_kms_helper]
 ? __drm_dbg+0x87/0x90 [drm]
 ? intel_dp_hpd_pulse+0x24b/0x400 [i915]
 intel_dp_hpd_pulse+0x24b/0x400 [i915]
 i915_digport_work_func+0xd6/0x160 [i915]
 process_one_work+0x1a9/0x370
 worker_thread+0x4d/0x3a0
 kthread+0xf9/0x130
 ? process_one_work+0x370/0x370
 ? kthread_park+0x90/0x90
 ret_from_fork+0x35/0x40

So, fix this.

Ugggh, what a fail! I found this in Feb and posted the patch in 20200218171522.GF253734@art_vandelay. I had to migrate my workstation due to WFH order and didn't apply the patch before pushing. Messy messy messy.

Thanks for fixing!

Reviewed-by: Sean Paul sean@poorly.run

Signed-off-by: Lyude Paul lyude@redhat.com Fixes: fbc821c4a506 ("drm/mst: Support simultaneous down replies") Cc: Wayne Lin Wayne.Lin@amd.com Cc: Lyude Paul lyude@redhat.com Cc: Wayne Lin waynelin@amd.com Cc: Sean Paul seanpaul@chromium.org

---

drivers/gpu/drm/drm_dp_mst_topology.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index 1ff49547b2e8..8751278b3941 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -3703,7 +3703,8 @@ static bool drm_dp_get_one_sb_msg(struct drm_dp_mst_topology_mgr *mgr, bool up, int basereg = up ? DP_SIDEBAND_MSG_UP_REQ_BASE : DP_SIDEBAND_MSG_DOWN_REP_BASE;

•   *mstb = NULL;
  

•   if (!up)
  

•           *mstb = NULL;
    *seqno = -1;
  
    len = min(mgr->max_dpcd_transaction_bytes, 16);
  

-- 2.25.1