Sorry, I realized there is a mistake in this patch after sending it out. It results in a use-after-free of "entry". I've sent out an updated version which should avoid the issue.
On 1/25/24 10:03, Erik Kurzinger wrote:
> During syncobj_eventfd_entry_func, dma_fence_chain_find_seqno may set
> the fence to NULL if the given seqno is signaled and a later seqno has
> already been submitted. In that case, the eventfd should be signaled
> immediately which currently does not happen.
>
> This is a similar issue to the one addressed by b19926d4f3a6
> ("drm/syncobj: Deal with signalled fences in drm_syncobj_find_fence")
>
> As a fix, if the return value of dma_fence_chain_find_seqno indicates
> success but it sets the fence to NULL, we should simply signal the
> eventfd immediately.
>
> Signed-off-by: Erik Kurzinger <ekurzinger@xxxxxxxxxx>
> Fixes: c7a472297169 ("drm/syncobj: add IOCTL to register an eventfd")
> ---
> drivers/gpu/drm/drm_syncobj.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index e04965878a08..cc3af1084950 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -1441,10 +1441,21 @@ syncobj_eventfd_entry_func(struct drm_syncobj *syncobj,
>
> /* This happens inside the syncobj lock */
> fence = dma_fence_get(rcu_dereference_protected(syncobj->fence, 1));
> + if (!fence)
> + return;
> +
> ret = dma_fence_chain_find_seqno(&fence, entry->point);
> - if (ret != 0 || !fence) {
> + if (ret != 0) {
> + /* The given seqno has not been submitted yet. */
> dma_fence_put(fence);
> return;
> + } else if (!fence) {
> + /* If dma_fence_chain_find_seqno returns 0 but sets the fence
> + * to NULL, it implies that the given seqno is signaled and a
> + * later seqno has already been submitted. Signal the eventfd
> + * immediately in that case. */
> + eventfd_signal(entry->ev_fd_ctx, 1);
> + syncobj_eventfd_entry_free(entry);
> }
>
> list_del_init(&entry->node);
