4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxx> commit 3792b7c1a70815fe4e954221c096f9278638fd21 upstream. 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 fence get/put dance and manipulate the list first (Chris Wilson) Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Signed-off-by: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxx> Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Link: https://patchwork.freedesktop.org/patch/msgid/20170729152217.8362-2-gustavo@xxxxxxxxxxx [s/dma_fence/fence/g - gregkh] Cc: Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/dma-buf/sw_sync.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) --- a/drivers/dma-buf/sw_sync.c +++ b/drivers/dma-buf/sw_sync.c @@ -213,11 +213,21 @@ static void sync_timeline_signal(struct obj->value += inc; list_for_each_entry_safe(pt, next, &obj->pt_list, link) { - if (!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(). + */ + fence_signal_locked(&pt->base); } spin_unlock_irq(&obj->lock);