Am 05.03.2018 um 08:55 schrieb Liu, Monk:
Hi Christian
You are right on that part of obj-staged is set to NULL in add_fence,
So my following question will be why we kfree(obj->staged) in reserve_shared() if staged is always NULL in that point ?
Good question, I haven't wrote code that so I can't fully answer.
Maybe Chris or Maarten know more about that.
Christian.
Thanks
/Monk
-----Original Message-----
From: Christian König [mailto:ckoenig.leichtzumerken@xxxxxxxxx]
Sent: 2018年2月28日 16:27
To: Liu, Monk <Monk.Liu@xxxxxxx>; dri-devel@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
Subject: Re: [PATCH] dma-buf/reservation: shouldn't kfree staged when slot available
Am 28.02.2018 um 07:44 schrieb Monk Liu:
under below scenario the obj->fence would refer to a wild pointer:
1,call reservation_object_reserved_shared
2,call reservation_object_add_shared_fence
3,call reservation_object_reserved_shared
4,call reservation_object_add_shared_fence
in step 1, staged is allocated,
in step 2, code path will go reservation_object_add_shared_replace()
and obj->fence would be assigned as staged (through RCU_INIT_POINTER)
in step 3, obj->staged will be freed(by simple kfree), which make
obj->fence point to a wild pointer...
Well that explanation is still nonsense. See
reservation_object_add_shared_fence:
obj->staged = NULL;
Among the first things reservation_object_add_shared_fence() does is it
sets obj->staged to NULL.
So step 3 will not free anything and we never have a wild pointer.
Regards,
Christian.
in step 4, code path will go reservation_object_add_shared_inplace()
and inside it the @fobj (which equals to @obj->staged, set by above steps)
is already a wild pointer
should remov the kfree on staged in reservation_object_reserve_shared()
Change-Id: If7c01f1b4be3d3d8a81efa90216841f79ab1fc1c
Signed-off-by: Monk Liu <Monk.Liu@xxxxxxx>
---
drivers/dma-buf/reservation.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c
index 375de41..b473ccc 100644
--- a/drivers/dma-buf/reservation.c
+++ b/drivers/dma-buf/reservation.c
@@ -74,12 +74,9 @@ int reservation_object_reserve_shared(struct reservation_object *obj)
old = reservation_object_get_list(obj);
if (old && old->shared_max) {
- if (old->shared_count < old->shared_max) {
- /* perform an in-place update */
- kfree(obj->staged);
- obj->staged = NULL;
+ if (old->shared_count < old->shared_max)
return 0;
- } else
+ else
max = old->shared_max * 2;
} else
max = 4;
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