From: Gustavo Padovan gustavo.padovan@collabora.com
If userspace already dropped its own reference by closing the sw_sync fence fd we might end up in a deadlock where dma_fence_is_signaled_locked() will trigger the release of the fence and thus try to hold the lock to remove the fence from the list.
dma_fence_is_signaled_locked() tries to release/free the fence and hold the lock in the process.
We fix that by changing the order operation and clean up the list and rb-tree first.
v2: Drop the fence get/put dance and manipulate the list first (Chris Wilson)
Cc: Chris Wilson chris@chris-wilson.co.uk Signed-off-by: Gustavo Padovan gustavo.padovan@collabora.com --- drivers/dma-buf/sw_sync.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c index ef0cc08..38cc738 100644 --- a/drivers/dma-buf/sw_sync.c +++ b/drivers/dma-buf/sw_sync.c @@ -213,11 +213,21 @@ static void sync_timeline_signal(struct sync_timeline *obj, unsigned int inc) obj->value += inc;
list_for_each_entry_safe(pt, next, &obj->pt_list, link) { - if (!dma_fence_is_signaled_locked(&pt->base)) + if (!timeline_fence_signaled(&pt->base)) break;
list_del_init(&pt->link); rb_erase(&pt->node, &obj->pt_tree); + + /* + * A signal callback may release the last reference to this + * fence, causing it to be freed. That operation has to be + * last to avoid a use after free inside this loop, and must + * be after we remove the fence from the timeline in order to + * prevent deadlocking on timeline->lock inside + * timeline_fence_release(). + */ + dma_fence_signal_locked(&pt->base); }
spin_unlock_irq(&obj->lock);