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).
If we always hold a reference for an unsignaled fence held by the
timeline, we no longer need to detach the fence from the timeline upon
release. This is only possible since commit ea4d5a270b57
("dma-buf/sw_sync: force signal all unsignaled fences on dying timeline")
where we introduced decoupling of the fences from the timeline upon release.
Reported-by: Bas Nieuwenhuizen <bas@xxxxxxxxxxxxxxxxxxx>
Fixes: d3c6dd1fb30d ("dma-buf/sw_sync: Synchronize signal vs syncpt free")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Gustavo Padovan <gustavo@xxxxxxxxxxx>
Cc: Christian König <christian.koenig@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
drivers/dma-buf/sw_sync.c | 32 +++++++-------------------------
1 file changed, 7 insertions(+), 25 deletions(-)
diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c
index 348b3a9170fa..4cc2ac03a84a 100644
--- a/drivers/dma-buf/sw_sync.c
+++ b/drivers/dma-buf/sw_sync.c
@@ -130,16 +130,7 @@ static const char *timeline_fence_get_timeline_name(struct dma_fence *fence)
static void timeline_fence_release(struct dma_fence *fence)
{
- struct sync_pt *pt = dma_fence_to_sync_pt(fence);
struct sync_timeline *parent = dma_fence_parent(fence);
- unsigned long flags;
-
- spin_lock_irqsave(fence->lock, flags);
- if (!list_empty(&pt->link)) {
- list_del(&pt->link);
- rb_erase(&pt->node, &parent->pt_tree);
- }
- spin_unlock_irqrestore(fence->lock, flags);
sync_timeline_put(parent);
dma_fence_free(fence);
@@ -203,18 +194,11 @@ static void sync_timeline_signal(struct sync_timeline *obj, unsigned int inc)
if (!timeline_fence_signaled(&pt->base))
break;
- list_del_init(&pt->link);
+ list_del(&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);
+ dma_fence_put(&pt->base);
}
spin_unlock_irq(&obj->lock);
@@ -261,13 +245,9 @@ static struct sync_pt *sync_pt_create(struct sync_timeline *obj,
} else if (cmp < 0) {
p = &parent->rb_left;
} else {
- if (dma_fence_get_rcu(&other->base)) {
- sync_timeline_put(obj);
- kfree(pt);
- pt = other;
- goto unlock;
- }
- p = &parent->rb_left;
+ dma_fence_put(&pt->base);
+ pt = other;
+ goto unlock;
}
}
rb_link_node(&pt->node, parent, p);
@@ -278,6 +258,7 @@ static struct sync_pt *sync_pt_create(struct sync_timeline *obj,
parent ? &rb_entry(parent, typeof(*pt), node)->link : &obj->pt_list);
}
unlock:
+ dma_fence_get(&pt->base); /* keep a ref for the timeline */
spin_unlock_irq(&obj->lock);
return pt;
@@ -316,6 +297,7 @@ static int sw_sync_debugfs_release(struct inode *inode, struct file *file)
list_for_each_entry_safe(pt, next, &obj->pt_list, link) {
dma_fence_set_error(&pt->base, -ENOENT);
dma_fence_signal_locked(&pt->base);
+ dma_fence_put(&pt->base);
}
spin_unlock_irq(&obj->lock);
--
2.20.1
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