[PATCH] dma-buf: Discard old fence_excl on retrying get_fences_rcu for realloc

[Koenig, Christian]

Am 04.06.19 um 14:39 schrieb Chris Wilson:
> If we have to drop the seqcount & rcu lock to perform a krealloc, we
> have to restart the loop. In doing so, be careful not to lose track of
> the already acquired exclusive fence.
>
> Fixes: fedf54132d24 ("dma-buf: Restart reservation_object_get_fences_rcu() after writes") #v4.10
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Cc: Christian König <christian.koenig at amd.com>
> Cc: Alex Deucher <alexander.deucher at amd.com>
> Cc: Sumit Semwal <sumit.semwal at linaro.org>
> Cc: stable at vger.kernel.org
> ---
>   drivers/dma-buf/reservation.c | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c
> index 4d32e2c67862..704503df4892 100644
> --- a/drivers/dma-buf/reservation.c
> +++ b/drivers/dma-buf/reservation.c
> @@ -365,6 +365,12 @@ int reservation_object_get_fences_rcu(struct reservation_object *obj,
>   					   GFP_NOWAIT | __GFP_NOWARN);
>   			if (!nshared) {
>   				rcu_read_unlock();
> +
> +				if (fence_excl) {
> +					dma_fence_put(fence_excl);
> +					fence_excl = NULL;
> +				}
> +

dma_fence_put is NULL save, so no need for the if.

But apart from that a good catch,
Christian.

>   				nshared = krealloc(shared, sz, GFP_KERNEL);
>   				if (nshared) {
>   					shared = nshared;