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authorChris Wilson <chris@chris-wilson.co.uk>2019-07-12 09:03:14 +0100
committerChris Wilson <chris@chris-wilson.co.uk>2019-07-16 21:02:39 +0100
commit30fe7b07f6cb7f391181eb9d2ea2687cd9bcf395 (patch)
tree850f2f651e97b32ef9b98a5fa637b8464821dac1 /drivers/dma-buf
parent45b2fda3d82d686cc014e4c485332f85e4bd64de (diff)
downloadlinux-30fe7b07f6cb7f391181eb9d2ea2687cd9bcf395.tar.bz2
dma-buf: Relax the write-seqlock for reallocating the shared fence list
As the set of shared fences is not being changed during reallocation of the reservation list, we can skip updating the write_seqlock. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: Christian König <christian.koenig@amd.com> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: https://patchwork.freedesktop.org/patch/msgid/20190712080314.21018-2-chris@chris-wilson.co.uk
Diffstat (limited to 'drivers/dma-buf')
-rw-r--r--drivers/dma-buf/reservation.c14
1 files changed, 7 insertions, 7 deletions
diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c
index 80ecc1283d15..c71b85c8c159 100644
--- a/drivers/dma-buf/reservation.c
+++ b/drivers/dma-buf/reservation.c
@@ -157,15 +157,15 @@ int reservation_object_reserve_shared(struct reservation_object *obj,
(ksize(new) - offsetof(typeof(*new), shared)) /
sizeof(*new->shared);
- preempt_disable();
- write_seqcount_begin(&obj->seq);
/*
- * RCU_INIT_POINTER can be used here,
- * seqcount provides the necessary barriers
+ * We are not changing the effective set of fences here so can
+ * merely update the pointer to the new array; both existing
+ * readers and new readers will see exactly the same set of
+ * active (unsignaled) shared fences. Individual fences and the
+ * old array are protected by RCU and so will not vanish under
+ * the gaze of the rcu_read_lock() readers.
*/
- RCU_INIT_POINTER(obj->fence, new);
- write_seqcount_end(&obj->seq);
- preempt_enable();
+ rcu_assign_pointer(obj->fence, new);
if (!old)
return 0;