Re: [PATCH] dma-buf/reservation: should keep later one in add fence(v2)

[zhoucm1 <zhoucm1@xxxxxxx>]

On 2018年03月06日 13:59, Liu, Monk wrote:
> >    
> > -		if (check->context == fence->context ||
> > +		if ((check->context == fence->context &&
> > +			dma_fence_is_later(fence, check)) ||
> We still need do more for !dma_fence_is_later(fence, check)   case, in which, we will don't need add new fence to resv slot.
>
> if ((check->context == fence->context) && dma_fence_is_later(fence, check))
>           fobj->shared_count = j;
>           RCU_INIT_POINTER(fobj->shared[fobj->shared_count], fence);
>           fobj->shared_count++;
> } else {
>           dma_fence_put(fence);
> }
>
> No you cannot do that, check is changed and not the one you want,
> Besides, we don't need to consider the case you mentioned, take only one fence in obj->staged for example:
>
> You add a fence whose context is equal to this fence (check), so current logic will put this check into fobj->shared[++j],
Yes, if !dma_fence_is_later(fence, check), then 'check' will be put to 
fobj->shared[++j], so we don't need add new fence to resv slot, don't we?

Regards,
David Zhou
> so in the end
> Obj->fence will point to fobj, and original old would be rcu_kfree()
>
> No additional action actually needed...
>
> /Monk
>
> -----Original Message-----
> From: Zhou, David(ChunMing)
> Sent: 2018年3月6日 12:25
> To: Liu, Monk <Monk.Liu@xxxxxxx>; dri-devel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH] dma-buf/reservation: should keep later one in add fence(v2)
>
>
>
> On 2018年03月06日 11:53, Monk Liu wrote:
> > v2:
> > still check context first to avoid warning from dma_fence_is_later
> > apply this fix in add_shared_replace as well
> >
> > Change-Id: If6a979ba9fd6c923b82212f35f07a9ff31c86767
> > Signed-off-by: Monk Liu <Monk.Liu@xxxxxxx>
> > ---
> >    drivers/dma-buf/reservation.c | 6 ++++--
> >    1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/dma-buf/reservation.c
> > b/drivers/dma-buf/reservation.c index 314eb10..c6e3c86 100644
> > --- a/drivers/dma-buf/reservation.c
> > +++ b/drivers/dma-buf/reservation.c
> > @@ -118,7 +118,8 @@ reservation_object_add_shared_inplace(struct reservation_object *obj,
> >    		old_fence = rcu_dereference_protected(fobj->shared[i],
> >    						reservation_object_held(obj));
> >    
> > -		if (old_fence->context == fence->context) {
> > +		if (old_fence->context == fence->context &&
> > +			dma_fence_is_later(fence, old_fence)) {
> >    			/* memory barrier is added by write_seqcount_begin */
> >    			RCU_INIT_POINTER(fobj->shared[i], fence);
> >    			write_seqcount_end(&obj->seq);
> > @@ -179,7 +180,8 @@ reservation_object_add_shared_replace(struct reservation_object *obj,
> >    		check = rcu_dereference_protected(old->shared[i],
> >    						reservation_object_held(obj));
> >    
> > -		if (check->context == fence->context ||
> > +		if ((check->context == fence->context &&
> > +			dma_fence_is_later(fence, check)) ||
> We still need do more for !dma_fence_is_later(fence, check)   case, in which, we will don't need add new fence to resv slot.
>
> if ((check->context == fence->context) && dma_fence_is_later(fence, check))
>           fobj->shared_count = j;
>           RCU_INIT_POINTER(fobj->shared[fobj->shared_count], fence);
>           fobj->shared_count++;
> } else {
>           dma_fence_put(fence);
> }
>
>
> Regards,
> David Zhou
> >    		    dma_fence_is_signaled(check))
> >    			RCU_INIT_POINTER(fobj->shared[--k], check);
> >    		else

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