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

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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 <[email protected]>
Signed-off-by: Gustavo Padovan <[email protected]>
Reviewed-by: Chris Wilson <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
This commit is contained in:
Gustavo Padovan 2017-07-29 12:22:16 -03:00
commit 3792b7c1a7
1 changed files with 11 additions and 1 deletions
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12
drivers/dma-buf/sw_sync.c
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@ -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);