On Fri, 30 Jun 2023 10:02:52 +0200 Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> wrote: > Hi Danilo, > > On Fri, 30 Jun 2023 00:25:18 +0200 > Danilo Krummrich <dakr@xxxxxxxxxx> wrote: > > > + * int driver_gpuva_remap(struct drm_gpuva_op *op, void *__ctx) > > + * { > > + * struct driver_context *ctx = __ctx; > > + * > > + * drm_gpuva_remap(ctx->prev_va, ctx->next_va, &op->remap); > > + * > > + * drm_gpuva_unlink(op->remap.unmap->va); > > + * kfree(op->remap.unmap->va); > > + * > > + * if (op->remap.prev) { > > + * drm_gpuva_link(ctx->prev_va); > > I ended up switching to dma_resv-based locking for the GEMs and I > wonder what the locking is supposed to look like in the async-mapping > case, where we insert/remove the VA nodes in the drm_sched::run_job() > path. > > What I have right now is something like: > > dma_resv_lock(vm->resv); > > // split done in drm_gpuva_sm_map(), each iteration > // of the loop is a call to the driver ->[re,un]map() > // hook > for_each_sub_op() { > > // Private BOs have their resv field pointing to the > // VM resv and we take the VM resv lock before calling > // drm_gpuva_sm_map() > if (vm->resv != gem->resv) > dma_resv_lock(gem->resv); > > drm_gpuva_[un]link(va); > gem_[un]pin(gem); > > if (vm->resv != gem->resv) > dma_resv_unlock(gem->resv); > } > > dma_resv_unlock(vm->resv); > > In practice, I don't expect things to deadlock, because the VM resv is > not supposed to be taken outside the VM context and the locking order > is always the same (VM lock first, and then each shared BO > taken/released independently), but I'm not super thrilled by this > nested lock, and I'm wondering if we shouldn't have a pass collecting > locks in a drm_exec context first, and then have > the operations executed. IOW, something like that: > > drm_exec_init(exec, DRM_EXEC_IGNORE_DUPLICATES) > drm_exec_until_all_locked(exec) { > // Dummy GEM is the dummy GEM object I use to make the VM > // participate in the locking without having to teach > // drm_exec how to deal with raw dma_resv objects. > ret = drm_exec_lock_obj(exec, vm->dummy_gem); > drm_exec_retry_on_contention(exec); > if (ret) > return ret; > > // Could take the form of drm_gpuva_sm_[un]map_acquire_locks() > // helpers > for_each_sub_op() { > ret = drm_exec_lock_obj(exec, gem); > if (ret) > return ret; > } > } > > // each iteration of the loop is a call to the driver > // ->[re,un]map() hook > for_each_sub_op() { > ... > gem_[un]pin_locked(gem); Just wanted to clarify that the pages have been pinned at VM_BIND job creation time, so this gem_pin_locked() call is effectively just a pin_count++, not the whole page allocation, which we don't want to happen in a dma-signaling path. > drm_gpuva_[un]link(va); > ... > } > > drm_exec_fini(exec);