Messages in this thread | | | Date | Fri, 18 Aug 2023 11:09:17 +0200 | Subject | Re: [Linaro-mm-sig] [PATCH] dma-buf/sw_sync: Avoid recursive lock during fence signal | From | Christian König <> |
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Am 17.08.23 um 23:37 schrieb Rob Clark: > From: Rob Clark <robdclark@chromium.org> > > 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). > > To avoid that, temporarily hold an extra reference to the signalled > fences until after we drop the lock. > > (This is an alternative implementation of https://patchwork.kernel.org/patch/11664717/ > which avoids some potential UAF issues with the original patch.) > > Reported-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl> > Fixes: d3c6dd1fb30d ("dma-buf/sw_sync: Synchronize signal vs syncpt free") > Signed-off-by: Rob Clark <robdclark@chromium.org> > --- > drivers/dma-buf/sw_sync.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c > index 63f0aeb66db6..ceb6a0408624 100644 > --- a/drivers/dma-buf/sw_sync.c > +++ b/drivers/dma-buf/sw_sync.c > @@ -191,6 +191,7 @@ static const struct dma_fence_ops timeline_fence_ops = { > */ > static void sync_timeline_signal(struct sync_timeline *obj, unsigned int inc) > { > + LIST_HEAD(signalled); > struct sync_pt *pt, *next; > > trace_sync_timeline(obj); > @@ -203,9 +204,13 @@ static void sync_timeline_signal(struct sync_timeline *obj, unsigned int inc) > if (!timeline_fence_signaled(&pt->base)) > break; > > + dma_fence_get(&pt->base);
Question is why don't have the fences a reference on the list in the first place?
> + > list_del_init(&pt->link); > rb_erase(&pt->node, &obj->pt_tree); > > + list_add_tail(&pt->link, &signalled);
Instead of list_del()/list_add_tail() you could also use list_move_tail() here.
> + > /* > * A signal callback may release the last reference to this > * fence, causing it to be freed. That operation has to be > @@ -218,6 +223,11 @@ static void sync_timeline_signal(struct sync_timeline *obj, unsigned int inc) > } > > spin_unlock_irq(&obj->lock); > + > + list_for_each_entry_safe(pt, next, &signalled, link) { > + list_del(&pt->link);
You must use list_del_init() here or otherwise the pt->link will keep pointing to the prev/next entries and the list_empty() check in timeline_fence_release() will fail and potentially corrupt things.
Regards, Christian.
> + dma_fence_put(&pt->base); > + } > } > > /**
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