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Commit aee58f4d authored by Rob Clark's avatar Rob Clark Committed by Greg Kroah-Hartman
Browse files

dma-buf/sw_sync: Avoid recursive lock during fence signal 

[ Upstream commit e531fdb5cd5ee2564b7fe10c8a9219e2b2fac61e ]

If a signal callback releases the sw_sync fence, that will trigger a
deadlock as the timeline_fence_release recurses onto the fence->lock
(used both for signaling and the the timeline tree).

To avoid that, temporarily hold an extra reference to the signalled
fences until after we drop the lock.

(This is an alternative implementation of https://patchwork.kernel.org/patch/11664717/


which avoids some potential UAF issues with the original patch.)

v2: Remove now obsolete comment, use list_move_tail() and
    list_del_init()

Reported-by: default avatarBas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Fixes: d3c6dd1fb30d ("dma-buf/sw_sync: Synchronize signal vs syncpt free")
Signed-off-by: default avatarRob Clark <robdclark@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230818145939.39697-1-robdclark@gmail.com


Reviewed-by: default avatarChristian König <christian.koenig@amd.com>
Signed-off-by: default avatarChristian König <christian.koenig@amd.com>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 92e79e1c

drivers/dma-buf/sw_sync.c

+9 −9
Original line number Diff line number Diff line
@@ -200,6 +200,7 @@ static const struct dma_fence_ops timeline_fence_ops = { 
 */

static void sync_timeline_signal(struct sync_timeline *obj, unsigned int inc)

{

	LIST_HEAD(signalled);

	struct sync_pt *pt, *next;



	trace_sync_timeline(obj);
@@ -212,21 +213,20 @@ static void sync_timeline_signal(struct sync_timeline *obj, unsigned int inc) 
		if (!timeline_fence_signaled(&pt->base))

			break;



		list_del_init(&pt->link);

		dma_fence_get(&pt->base);



		list_move_tail(&pt->link, &signalled);

		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);



	list_for_each_entry_safe(pt, next, &signalled, link) {

		list_del_init(&pt->link);

		dma_fence_put(&pt->base);

	}

}



/**