Quoting Chunming Zhou (2018-10-22 10:08:59)
> v2:
> add a mutex between sync_cb execution and free.
> v3:
> clearly separating the roles for pt_lock and cb_mutex (Chris)
>
> Signed-off-by: Chunming Zhou <david1.zhou@xxxxxxx>
> Cc: Daniel Vetter <daniel@xxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Christian König <christian.koenig@xxxxxxx>
> ---
> drivers/gpu/drm/drm_syncobj.c | 51 ++++++++++++++++++-----------------
> include/drm/drm_syncobj.h | 8 ++++--
> 2 files changed, 33 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index 57bf6006394d..827d2ea5bb79 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -125,23 +125,24 @@ static int drm_syncobj_fence_get_or_add_callback(struct drm_syncobj *syncobj,
> if (!ret)
> return 1;
>
> - spin_lock(&syncobj->lock);
> + spin_lock(&syncobj->pt_lock);
> /* We've already tried once to get a fence and failed. Now that we
> * have the lock, try one more time just to be sure we don't add a
> * callback when a fence has already been set.
> */
> if (!list_empty(&syncobj->signal_pt_list)) {
> - spin_unlock(&syncobj->lock);
> + spin_unlock(&syncobj->pt_lock);
> drm_syncobj_search_fence(syncobj, 0, 0, fence);
> if (*fence)
> return 1;
> - spin_lock(&syncobj->lock);
> } else {
> + spin_unlock(&syncobj->pt_lock);
> *fence = NULL;
> + mutex_lock(&syncobj->cb_mutex);
> drm_syncobj_add_callback_locked(syncobj, cb, func);
> + mutex_unlock(&syncobj->cb_mutex);
There's no guard should the fence be installed after our check but before
we add the callback. Aiui, the cb_mutex should be taken outside of the
pt_lock around this if() block.
> ret = 0;
> }
> - spin_unlock(&syncobj->lock);
>
> return ret;
> }
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