From 3792b7c1a70815fe4e954221c096f9278638fd21 Mon Sep 17 00:00:00 2001
From: Gustavo Padovan <gustavo.padovan@collabora.com>
Date: Sat, 29 Jul 2017 12:22:16 -0300
Subject: [PATCH] dma-buf/sw_sync: clean up list before signaling the fence
Git-commit: 3792b7c1a70815fe4e954221c096f9278638fd21
Patch-mainline: v4.14-rc1
References: bsc#794563
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
Acked-by: Takashi Iwai <tiwai@suse.de>
---
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 ef0cc08f5dfb..38cc7389a6c1 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);
--
2.20.1