On Fri, 2026-02-13 at 15:27 +0100, Boris Brezillon wrote: > On Tue, 10 Feb 2026 11:01:59 +0100 > "Christian König" <[email protected]> wrote: > > > Implement per-fence spinlocks, allowing implementations to not give an > > external spinlock to protect the fence internal statei. Instead a spinlock > > embedded into the fence structure itself is used in this case. > > > > Shared spinlocks have the problem that implementations need to guarantee > > that the lock live at least as long all fences referencing them. > > > > Using a per-fence spinlock allows completely decoupling spinlock producer > > and consumer life times, simplifying the handling in most use cases. > > > > v2: improve naming, coverage and function documentation > > v3: fix one additional locking in the selftests > > v4: separate out some changes to make the patch smaller, > > fix one amdgpu crash found by CI systems > > > > Signed-off-by: Christian König <[email protected]> > > --- > > drivers/dma-buf/dma-fence.c | 21 ++++++++++++++++----- > > drivers/dma-buf/sync_debug.h | 2 +- > > drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h | 2 +- > > drivers/gpu/drm/drm_crtc.c | 2 +- > > drivers/gpu/drm/drm_writeback.c | 2 +- > > drivers/gpu/drm/nouveau/nouveau_fence.c | 3 ++- > > drivers/gpu/drm/qxl/qxl_release.c | 3 ++- > > drivers/gpu/drm/vmwgfx/vmwgfx_fence.c | 3 ++- > > drivers/gpu/drm/xe/xe_hw_fence.c | 3 ++- > > include/linux/dma-fence.h | 19 +++++++++++++------ > > 10 files changed, 41 insertions(+), 19 deletions(-) > > > > diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c > > index 56aa59867eaa..1833889e7466 100644 > > --- a/drivers/dma-buf/dma-fence.c > > +++ b/drivers/dma-buf/dma-fence.c > > @@ -343,7 +343,6 @@ void __dma_fence_might_wait(void) > > } > > #endif > > > > - > > /** > > * dma_fence_signal_timestamp_locked - signal completion of a fence > > * @fence: the fence to signal > > @@ -1067,7 +1066,6 @@ static void > > __dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops, > > spinlock_t *lock, u64 context, u64 seqno, unsigned long flags) > > { > > - BUG_ON(!lock); > > BUG_ON(!ops || !ops->get_driver_name || !ops->get_timeline_name); > > > > kref_init(&fence->refcount); > > @@ -1078,10 +1076,15 @@ __dma_fence_init(struct dma_fence *fence, const > > struct dma_fence_ops *ops, > > */ > > RCU_INIT_POINTER(fence->ops, ops); > > INIT_LIST_HEAD(&fence->cb_list); > > - fence->lock = lock; > > fence->context = context; > > fence->seqno = seqno; > > fence->flags = flags | BIT(DMA_FENCE_FLAG_INITIALIZED_BIT); > > + if (lock) { > > + fence->extern_lock = lock; > > + } else { > > + spin_lock_init(&fence->inline_lock); > > + fence->flags |= BIT(DMA_FENCE_FLAG_INLINE_LOCK_BIT); > > Hm, does this even make a different in term of instructions to check for > a bit instead of extern_lock == NULL? If not, I'd be in favor of > killing this redundancy and checking extern_lock against NULL in > dma_fence_spinlock().
extern_lock and inline_lock are a union, so they overlap each other. inline_lock will only be equivalent to all zeros after initializing a new fence to 0. P. PS: Can you terminate messages by a delimiter or by cropping? I give this tip sometimes, because often the reviewer has to scroll emails down to the end to see whether there are further comments. I terminate my messages with "P." for that purpose ;]
