Reviewed-by: Lyude Paul <[email protected]> On Thu, 2026-08-13 at 01:13 +0200, Marek Czernohous wrote: > From: Marek Czernohous <[email protected]> > > nouveau_channel_del() tears the fence context down first and only > drops > the channel-kill subscription later, in the middle of the nvif object > teardown: > > if (chan->fence) > nouveau_fence(chan->cli->drm)->context_del(chan); > ... > nvif_object_dtor(&chan->vram); > nvif_event_dtor(&chan->kill); > > The subscribed handler is nouveau_channel_killed(), which calls > nouveau_channel_kill() and from there nouveau_fence_context_kill() on > chan->fence. A kill event delivered in that window takes fctx->lock > and > walks fctx->pending on a fence context that context_del() has already > freed. > > Nothing reaches this below Fermi today, because the subscription is > gated on FERMI_CHANNEL_GPFIFO and nothing kills a channel there. On > Fermi and newer the window is real but narrow, since a kill has to > land > exactly while the channel is being destroyed. That is reason enough > on > its own, which is why this carries a Fixes: tag. The last patch in > this > series subscribes Tesla channels as well; nothing kills those today, > so > it does not widen the exposure now, but it is the groundwork for a > recovery path that would, and the ordering is better fixed before > that > lands than alongside it. > > Drop the subscription before anything it depends on is torn down. > > Fixes: ea13e5abf807 ("drm/nouveau: signal pending fences when channel > has been killed") > Cc: [email protected] > Assisted-by: Claude:claude-opus-5 > Signed-off-by: Marek Czernohous <[email protected]> > --- > drivers/gpu/drm/nouveau/nouveau_chan.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/nouveau/nouveau_chan.c > b/drivers/gpu/drm/nouveau/nouveau_chan.c > index 598513f60449..f142f6310596 100644 > --- a/drivers/gpu/drm/nouveau/nouveau_chan.c > +++ b/drivers/gpu/drm/nouveau/nouveau_chan.c > @@ -90,6 +90,14 @@ nouveau_channel_del(struct nouveau_channel > **pchan) > { > struct nouveau_channel *chan = *pchan; > if (chan) { > + /* > + * Drop the kill-event subscription first. Its > handler > + * dereferences chan->fence, which the fence context > teardown > + * below frees, so leaving it armed across the > teardown leaves > + * a window for a use-after-free. > + */ > + nvif_event_dtor(&chan->kill); > + > if (chan->fence) > nouveau_fence(chan->cli->drm)- > >context_del(chan); > > @@ -100,7 +108,6 @@ nouveau_channel_del(struct nouveau_channel > **pchan) > nvif_object_dtor(&chan->nvsw); > nvif_object_dtor(&chan->gart); > nvif_object_dtor(&chan->vram); > - nvif_event_dtor(&chan->kill); > nvif_object_dtor(&chan->user); > nvif_mem_dtor(&chan->mem_userd); > nouveau_vma_del(&chan->sema.vma);
