Stocks are tumbling and oil is getting slammed

Traders and investors are back from their long holiday weekend.

Well, at least some of them are.

On what's expected to be a low volume day, stocks are in the red.

The Dow is down 110 points (0.6%), the S&P 500 is down 15 points (0.7%), and the Nasdaq is down 46 points (0.9%).

This follows a 2.6% tumble overnight in China's Shanghai Composite index.

Oil prices remain volatile with WTI crude down 3.6% and Brent crude down 3.3%.

Meanwhile, things are still crappy in the Texas economy. The Dallas Fed's general business activity index collapsed to -20.1 in December from -4.9 in November. The index, which has been in contraction territory all year, was much worse than the -7.0 expected by economists.

"The price of oil is really impacting our customer base and, in turn, purchases of our product," said a survey respondent in the fabricated metal products business. "It is getting ugly."

Among the major movers are Fitbit, the wearable health technology company. Fitbit is the top app in Apple's App Store, suggesting huge holiday sales.

FIT is up 3% in early trading.

On the losing side is Valeant Pharmaceuticals, which was down 9.5% in early trading.

Following reports that its CEO Mike Pearson was being treated for a severe case of pneumonia, Valeant announced that Pearson was officially taking a medical leave of absence.

That's about it.