Am 12.08.19 um 17:42 schrieb Chris Wilson:
> During release of the syncpt, we remove it from the list of syncpt and
> the tree, but only if it is not already been removed. However, during
> signaling, we first remove the syncpt from the list. So, if we
> concurrently free and signal the syncpt, the free may decide that it is
> not part of the tree and immediately free itself -- meanwhile the
> signaler goes onto to use the now freed datastructure.
>
> In particular, we get struct by commit 0e2f733addbf ("dma-buf: make
> dma_fence structure a bit smaller v2") as the cb_list is immediately
> clobbered by the kfree_rcu.
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111381
> Fixes: d3862e44daa7 ("dma-buf/sw-sync: Fix locking around sync_timeline lists")
> References: 0e2f733addbf ("dma-buf: make dma_fence structure a bit smaller v2")
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
> Cc: Sean Paul <seanpaul@xxxxxxxxxxxx>
> Cc: Gustavo Padovan <gustavo@xxxxxxxxxxx>
> Cc: Christian König <christian.koenig@xxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.14+
Acked-by: Christian König <christian.koenig@xxxxxxx>
> ---
> drivers/dma-buf/sw_sync.c | 13 +++++--------
> 1 file changed, 5 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c
> index 051f6c2873c7..27b1d549ed38 100644
> --- a/drivers/dma-buf/sw_sync.c
> +++ b/drivers/dma-buf/sw_sync.c
> @@ -132,17 +132,14 @@ 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)) {
> - 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);
> + 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);
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