[Intel-gfx] [PATCH] drm: fix deadlock of syncobj v5

[Koenig, Christian]

Am 23.10.18 um 11:11 schrieb Chris Wilson:
> Quoting zhoucm1 (2018-10-23 10:09:01)
>>
>> On 2018年10月23日 17:01, Chris Wilson wrote:
>>> Quoting Chunming Zhou (2018-10-23 08:57:54)
>>>> v2:
>>>> add a mutex between sync_cb execution and free.
>>>> v3:
>>>> clearly separating the roles for pt_lock and cb_mutex (Chris)
>>>> v4:
>>>> the cb_mutex should be taken outside of the pt_lock around this if() block. (Chris)
>>>> v5:
>>>> fix a corner case
>>>>
>>>> Tested by syncobj_basic and syncobj_wait of igt.
>>>>
>>>> Signed-off-by: Chunming Zhou <david1.zhou at amd.com>
>>>> Cc: Daniel Vetter <daniel at ffwll.ch>
>>>> Cc: Chris Wilson <chris at chris-wilson.co.uk>
>>>> Cc: Christian König <christian.koenig at amd.com>
>>>> Cc: intel-gfx at lists.freedesktop.org
>>>> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
>>>> ---
>>>>    drivers/gpu/drm/drm_syncobj.c | 55 +++++++++++++++++++----------------
>>>>    include/drm/drm_syncobj.h     |  8 +++--
>>>>    2 files changed, 36 insertions(+), 27 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
>>>> index 57bf6006394d..679a56791e34 100644
>>>> --- a/drivers/gpu/drm/drm_syncobj.c
>>>> +++ b/drivers/gpu/drm/drm_syncobj.c
>>>> @@ -125,23 +125,26 @@ static int drm_syncobj_fence_get_or_add_callback(struct drm_syncobj *syncobj,
>>>>           if (!ret)
>>>>                   return 1;
>>>>    
>>>> -       spin_lock(&syncobj->lock);
>>>> +       mutex_lock(&syncobj->cb_mutex);
>>>>           /* 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.
>>>>            */
>>>> +       spin_lock(&syncobj->pt_lock);
>>>>           if (!list_empty(&syncobj->signal_pt_list)) {
>>>> -               spin_unlock(&syncobj->lock);
>>>> +               spin_unlock(&syncobj->pt_lock);
>>>>                   drm_syncobj_search_fence(syncobj, 0, 0, fence);
>>> Hmm, just thinking of other ways of tidying this up
>>>
>>> mutex_lock(cb_lock);
>>> spin_lock(pt_lock);
>>> *fence = drm_syncobj_find_signal_pt_for_point();
>>> spin_unlock(pt_list);
>>> if (*!fence)
>>>        drm_syncobj_add_callback_locked(syncobj, cb, func);
>>> mutex_unlock(cb_lock);
>>>
>>> i.e. get rid of the early return and we can even drop the int return here
>>> as it is unimportant and unused.
>> Yes, do you need I send v6? or you make a separate patch as a improvment?
> Send it in reply, we still have some time before the shards catch up
> with the ml ;)

I'm idle anyway because I've locked myself out of the AMD VPN accidentally.

So just send me a ping when the v6 is ready to be committed and I can 
push it to drm-misc-next.

Christian.

> -Chris