Commit 3792b7c1 authored Jul 29, 2017 by Gustavo Padovan

dma-buf/sw_sync: clean up list before signaling the fence



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@chris-wilson.co.uk>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20170729152217.8362-2-gustavo@padovan.org

parent 150b6a9d

drivers/dma-buf/sw_sync.c

+11 −1

Original line number	Diff line number	Diff line
		@@ -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);