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drm/nouveau: unsubscribe the channel-kill event before the fence context

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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: ea13e5abf8 ("drm/nouveau: signal pending fences when channel has been killed")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5
Signed-off-by: Marek Czernohous <marek@czernohous.de>
Fixes: ea13e5abf8 ("drm/nouveau: signal pending fences when channel has been killed")
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patch.msgid.link/20260812231330.705425-2-mczernohous@gmail.com
This commit is contained in:
Marek Czernohous 2026-08-13 01:13:27 +02:00 committed by Lyude Paul
parent dc14753664
commit 511585987d
1 changed files with 8 additions and 1 deletions
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9
drivers/gpu/drm/nouveau/nouveau_chan.c
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@ -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);