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    Subject[PATCH 3.19.y-ckt 122/155] drm: fix mutex leak in drm_dp_get_mst_branch_device
    Date
    3.19.8-ckt10 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Adam Richter <adamrichter4@gmail.com>

    commit 30730c7f5943b3beace1e29f7f1476e05de3da14 upstream.

    In Linux 4.3-rc5, there is an error case in drm_dp_get_branch_device
    that returns without releasing mgr->lock, resulting a spew of kernel
    messages about a kernel work function possibly having leaked a mutex
    and presumably more serious adverse consequences later. This patch
    changes the error to "goto out" to unlock the mutex before returning.

    [airlied: grabbed from drm-next as it fixes something we've seen]

    Signed-off-by: Adam J. Richter <adam_richter2004@yahoo.com>
    Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
    Signed-off-by: Dave Airlie <airlied@redhat.com>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    drivers/gpu/drm/drm_dp_mst_topology.c | 7 ++++---
    1 file changed, 4 insertions(+), 3 deletions(-)

    diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
    index 1133179..df0fccb 100644
    --- a/drivers/gpu/drm/drm_dp_mst_topology.c
    +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
    @@ -1189,17 +1189,18 @@ static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_

    list_for_each_entry(port, &mstb->ports, next) {
    if (port->port_num == port_num) {
    - if (!port->mstb) {
    + mstb = port->mstb;
    + if (!mstb) {
    DRM_ERROR("failed to lookup MSTB with lct %d, rad %02x\n", lct, rad[0]);
    - return NULL;
    + goto out;
    }

    - mstb = port->mstb;
    break;
    }
    }
    }
    kref_get(&mstb->kref);
    +out:
    mutex_unlock(&mgr->lock);
    return mstb;
    }
    --
    1.9.1


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