Quoting Christian König (2019-08-07 14:53:12)
The only remaining use for this is to protect against setting a new exclusive fence while we grab both exclusive and shared. That can also be archived by looking if the exclusive fence has changed or not after completing the operation.
v2: switch setting excl fence to rcu_assign_pointer
Signed-off-by: Christian König christian.koenig@amd.com
drivers/dma-buf/reservation.c | 24 +++++------------------- include/linux/reservation.h | 9 ++------- 2 files changed, 7 insertions(+), 26 deletions(-)
diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c index 90bc6ef03598..f7f4a0858c2a 100644 --- a/drivers/dma-buf/reservation.c +++ b/drivers/dma-buf/reservation.c @@ -49,12 +49,6 @@ DEFINE_WD_CLASS(reservation_ww_class); EXPORT_SYMBOL(reservation_ww_class); -struct lock_class_key reservation_seqcount_class; -EXPORT_SYMBOL(reservation_seqcount_class);
-const char reservation_seqcount_string[] = "reservation_seqcount"; -EXPORT_SYMBOL(reservation_seqcount_string);
/**
- reservation_object_list_alloc - allocate fence list
- @shared_max: number of fences we need space for
@@ -103,9 +97,6 @@ static void reservation_object_list_free(struct reservation_object_list *list) void reservation_object_init(struct reservation_object *obj) { ww_mutex_init(&obj->lock, &reservation_ww_class);
__seqcount_init(&obj->seq, reservation_seqcount_string,&reservation_seqcount_class); RCU_INIT_POINTER(obj->fence, NULL); RCU_INIT_POINTER(obj->fence_excl, NULL);} @@ -282,12 +273,10 @@ void reservation_object_add_excl_fence(struct reservation_object *obj, dma_fence_get(fence); preempt_disable();
write_seqcount_begin(&obj->seq);/* write_seqcount_begin provides the necessary memory barrier */RCU_INIT_POINTER(obj->fence_excl, fence);
rcu_assign_pointer(obj->fence_excl, fence);/* pointer update must be visible before we modify the shared_count */ if (old)
old->shared_count = 0;write_seqcount_end(&obj->seq);
smp_store_mb(old->shared_count, 0); preempt_enable();/* inplace update, no shared fences */ @@ -368,11 +357,8 @@ int reservation_object_copy_fences(struct reservation_object *dst, old = reservation_object_get_excl(dst); preempt_disable();
write_seqcount_begin(&dst->seq);/* write_seqcount_begin provides the necessary memory barrier */RCU_INIT_POINTER(dst->fence_excl, new);RCU_INIT_POINTER(dst->fence, dst_list);write_seqcount_end(&dst->seq);
rcu_assign_pointer(dst->fence_excl, new);rcu_assign_pointer(dst->fence, dst_list); preempt_enable();reservation_object_list_free(src_list); diff --git a/include/linux/reservation.h b/include/linux/reservation.h index 044a5cd4af50..fd29baad0be3 100644 --- a/include/linux/reservation.h +++ b/include/linux/reservation.h @@ -46,8 +46,6 @@ #include <linux/rcupdate.h> extern struct ww_class reservation_ww_class; -extern struct lock_class_key reservation_seqcount_class; -extern const char reservation_seqcount_string[]; /**
- struct reservation_object_list - a list of shared fences
@@ -71,7 +69,6 @@ struct reservation_object_list { */ struct reservation_object { struct ww_mutex lock;
seqcount_t seq;struct dma_fence __rcu *fence_excl; struct reservation_object_list __rcu *fence; @@ -156,14 +153,12 @@ reservation_object_fences(struct reservation_object *obj, struct reservation_object_list **list, u32 *shared_count) {
unsigned int seq;do {seq = read_seqcount_begin(&obj->seq); *excl = rcu_dereference(obj->fence_excl); *list = rcu_dereference(obj->fence); *shared_count = *list ? (*list)->shared_count : 0;} while (read_seqcount_retry(&obj->seq, seq));
smp_rmb(); /* See reservation_object_add_excl_fence */} while (rcu_access_pointer(obj->fence_excl) != *excl);}
Reviewed-by: Chris Wilson chris@chris-wilson.co.uk
I think this is correct. Now see if we can convince Daniel! -Chris