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    Subject[PATCH 5.3 073/105] drm: damage_helper: Fix race checking plane->state->fb
    Date
    From: Sean Paul <seanpaul@chromium.org>

    commit 354c2d310082d1c384213ba76c3757dd3cd8755d upstream.

    Since the dirtyfb ioctl doesn't give us any hints as to which plane is
    scanning out the fb it's marking as damaged, we need to loop through
    planes to find it.

    Currently we just reach into plane state and check, but that can race
    with another commit changing the fb out from under us. This patch locks
    the plane before checking the fb and will release the lock if the plane
    is not displaying the dirty fb.

    Fixes: b9fc5e01d1ce ("drm: Add helper to implement legacy dirtyfb")
    Cc: Rob Clark <robdclark@gmail.com>
    Cc: Deepak Rawat <drawat@vmware.com>
    Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
    Cc: Thomas Hellstrom <thellstrom@vmware.com>
    Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
    Cc: Maxime Ripard <maxime.ripard@bootlin.com>
    Cc: Sean Paul <sean@poorly.run>
    Cc: David Airlie <airlied@linux.ie>
    Cc: Daniel Vetter <daniel@ffwll.ch>
    Cc: dri-devel@lists.freedesktop.org
    Cc: <stable@vger.kernel.org> # v5.0+
    Reported-by: Daniel Vetter <daniel@ffwll.ch>
    Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
    Signed-off-by: Sean Paul <seanpaul@chromium.org>
    Link: https://patchwork.freedesktop.org/patch/msgid/20190904202938.110207-1-sean@poorly.run
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/gpu/drm/drm_damage_helper.c | 8 +++++++-
    1 file changed, 7 insertions(+), 1 deletion(-)

    --- a/drivers/gpu/drm/drm_damage_helper.c
    +++ b/drivers/gpu/drm/drm_damage_helper.c
    @@ -212,8 +212,14 @@ retry:
    drm_for_each_plane(plane, fb->dev) {
    struct drm_plane_state *plane_state;

    - if (plane->state->fb != fb)
    + ret = drm_modeset_lock(&plane->mutex, state->acquire_ctx);
    + if (ret)
    + goto out;
    +
    + if (plane->state->fb != fb) {
    + drm_modeset_unlock(&plane->mutex);
    continue;
    + }

    plane_state = drm_atomic_get_plane_state(state, plane);
    if (IS_ERR(plane_state)) {

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