🐛 Bug

I'm reopening #1356 because I'm getting this error running my code on grid.ai.

I am getting error:

wandb.errors.error.Error: You must call wandb.init() before wandb.log()

Please reproduce using the BoringModel

Not possible since colab has only one GPU, unlike grid.ai

To Reproduce

On grid.ai or multiple GPU machine, create a trainer with WandbLogger and do not specify an accelerator. Run with gpus=-1 and hit this error.

Despite #2029 the default is ddp_spawn, which triggers this error on grid.ai:

/opt/conda/lib/python3.7/site-packages/pytorch_lightning/utilities/distributed.py:52: UserWarning: You requested multiple GPUs but did not specify a backend, e.g. `Trainer(accelerator="dp"|"ddp"|"ddp2")`. Setting `accelerator="ddp_spawn"` for you.

Workaround:

1. In main, run

import wandb
wandb.init(project...)

(seems redudant and potentially dangerous/foot-gunny since you are already passing a WandbLogger to the trainer.

2. Make sure trainer has accelerator=ddp defined.

Expected behavior

wandb logger works when trainer is given WandbLogger, gpu=-1, and no accelerator is defined, nor is a duplicate wandb init needed to be called.

Environment

grid.ai

• CUDA:
  - GPU:
  - Tesla M60
  - Tesla M60
  - available: True
  - version: 10.2
• Packages:
  - numpy: 1.20.2
  - pyTorch_debug: False
  - pyTorch_version: 1.8.1+cu102
  - pytorch-lightning: 1.2.7
  - tqdm: 4.60.0
• System:
  - OS: Linux
  - architecture:
  - 64bit
  -
  - processor: x86_64
  - python: 3.7.10
  - version: Proposal for help #1 SMP Tue Mar 16 04:56:19 UTC 2021