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authorChristian König <christian.koenig@amd.com>2021-11-11 17:18:34 +0300
committerChristian König <christian.koenig@amd.com>2022-04-01 14:30:10 +0300
commit15325e3c1013035c2e3e266ba79a0c3bef905f25 (patch)
tree7133f87d85a29cbf13d4d83dae57174d1b74f07a /drivers/dma-buf/dma-resv.c
parent3d7039e1e64980a5eb424373b3a5843b7d7891aa (diff)
downloadlinux-15325e3c1013035c2e3e266ba79a0c3bef905f25.tar.xz
dma-buf: drop the DAG approach for the dma_resv object v3
So far we had the approach of using a directed acyclic graph with the dma_resv obj. This turned out to have many downsides, especially it means that every single driver and user of this interface needs to be aware of this restriction when adding fences. If the rules for the DAG are not followed then we end up with potential hard to debug memory corruption, information leaks or even elephant big security holes because we allow userspace to access freed up memory. Since we already took a step back from that by always looking at all fences we now go a step further and stop dropping the shared fences when a new exclusive one is added. v2: Drop some now superflous documentation v3: Add some more documentation for the new handling. Signed-off-by: Christian König <christian.koenig@amd.com> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: https://patchwork.freedesktop.org/patch/msgid/20220321135856.1331-11-christian.koenig@amd.com
Diffstat (limited to 'drivers/dma-buf/dma-resv.c')
-rw-r--r--drivers/dma-buf/dma-resv.c16
1 files changed, 1 insertions, 15 deletions
diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
index 5001e9b4420a..be65522f0f47 100644
--- a/drivers/dma-buf/dma-resv.c
+++ b/drivers/dma-buf/dma-resv.c
@@ -351,35 +351,21 @@ EXPORT_SYMBOL(dma_resv_replace_fences);
* @fence: the exclusive fence to add
*
* Add a fence to the exclusive slot. @obj must be locked with dma_resv_lock().
- * Note that this function replaces all fences attached to @obj, see also
- * &dma_resv.fence_excl for a discussion of the semantics.
+ * See also &dma_resv.fence_excl for a discussion of the semantics.
*/
void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence)
{
struct dma_fence *old_fence = dma_resv_excl_fence(obj);
- struct dma_resv_list *old;
- u32 i = 0;
dma_resv_assert_held(obj);
- old = dma_resv_shared_list(obj);
- if (old)
- i = old->shared_count;
-
dma_fence_get(fence);
write_seqcount_begin(&obj->seq);
/* write_seqcount_begin provides the necessary memory barrier */
RCU_INIT_POINTER(obj->fence_excl, fence);
- if (old)
- old->shared_count = 0;
write_seqcount_end(&obj->seq);
- /* inplace update, no shared fences */
- while (i--)
- dma_fence_put(rcu_dereference_protected(old->shared[i],
- dma_resv_held(obj)));
-
dma_fence_put(old_fence);
}
EXPORT_SYMBOL(dma_resv_add_excl_fence);