• 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], 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@amd.com; dri-devel@freedesktop.org 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@amd.com

---

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

Make sense, will give v3

-----Original Message----- From: Zhou, David(ChunMing) Sent: 2018年3月6日 14:08 To: Liu, Monk Monk.Liu@amd.com; Zhou, David(ChunMing) David1.Zhou@amd.com; dri-devel@freedesktop.org Subject: Re: [PATCH] dma-buf/reservation: should keep later one in add fence(v2)

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@amd.com; dri-devel@freedesktop.org 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@amd.com

---

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

okay

________________________________ From: Chris Wilson chris@chris-wilson.co.uk Sent: Tuesday, March 6, 2018 4:24:21 PM To: Liu, Monk; dri-devel@freedesktop.org Cc: Liu, Monk Subject: Re: [PATCH] dma-buf/reservation: should keep later one in add fence(v2)

Quoting Monk Liu (2018-03-06 03:53:10)

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@amd.com

---

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)) {
  

This should be true by construction. Adding an older fence on the same context is a programming bug, imo. Between different callers the resv should have been locked and the fenced operations serialised, from the same caller, you shouldn't be handling more than one output fence? -Chris