Why would there be locks on the outside of a pantry?

I think the ghost opened the door. There is no other explanation.

1) The Problem With "Danny Did It" Theories

Danny COULD have opened the door, but there is no reason given in the film why he would do so. Danny in his normal state I could MAYBE see letting Jack out due to sympathy if his Dad sweet talked him into it. But Danny was in Tony mode so this seems less likely, being in a semi-catatonic state. Besides, Tony is the one warning Danny about the danger, so why would Tony make Danny open the door? Regardless of whether you think Tony is Danny form the future, a guardian spirit, or Danny's subconscious (that can admit the reality of Jack's abuse), why would Danny open the door in that state knowing what he knows?

2) The Problem With "Emergency LOCK Release" Theories

The fact is the bolt would still keep the door from opening even if there was an emergency lock release. Yet we KNOW the main pantry door was opened (by someone or something) because we see it open later in the movie when Jack goes on his axe rampage. We know he didn't chop his way out, because the door and the locks are clearly shown as being intact and undamaged later. He may not have even had the axe yet anyway. He would have still needed outside help to get the bolt open, so we are right back where we started from.

3) The Problem With "Side Exit" Theories

If there was a side door, the only reason Jack would have opened up the main door afterwards would be to get closer to the kitchen, and the only reason for going back into the pantry that I can think of is for food. But he's already eaten some snacks inside the pantry, so it's not like he's starving. Jack is a man on a mission, so how likely is it he fixed himself some dinner first? What did he say: "I'm gonna kill my wife and child, but I'm not just gonna kill them, I'm gonna chop them up into little pieces... but first, hamburgers!"?

Why would Jack bother opening the main door? The locks are clearly troublesome to work with, so why would he even bother with them once he got out? This clearly shows he was stuck inside the pantry for a while, because how long would it have taken him to find the side door and get out? As I said before, he was eating snacks inside the pantry, which he wouldn't do if he could get out easily. And even if there was an emergency lock release, the fact that he was trapped for a long time and raided the kitchen for snacks proves that he got out neither of those ways, but needed outside help.

4) The Problem With "Spatial Anomaly" Theories

It's true that the hotel layout keeps changing and moving around in impossible angles, and it does appear in Halloran's tour of the kitchen that there could be a side door. However, since the hotel and maze layouts are constantly changing throughout the whole film who's to say they didn't change again? Even if there was a side door and it was still there, I still don't know why he would open the other one once he got out. The mental picture of Jack making himself a nice pre-massacre candlelight dinner for one is too silly to contemplate. Jack opening the door through telekinesis is not supported by anything we see or hear in the film about shining ability, nor is there any indication Jack has those abilities. Finally, Kubrick himself said it was the ghost that opened the door. The inevitable conclusion: someone else opened the main pantry door... not Jack, probably the ghost or the faint possibility of Danny.

To recap: There was no side door and he couldn't get out even if there was an emergency lock release because of the bolt lock; we know the front door was open because we see it opened and undamaged later; finally, we know he was stuck in there quite a while because he was eating snacks and waiting listlessly for someone to let him out, indicating he had given up trying; Danny could have opened the door but lacked a clear motive; Jack could have "shined it open" but nothing in the film support this.

I never noticed that padlock hanging there before. Good catch, that does make it interesting. I did watch the sequence just now of her opening the deadbolt about 10 times and I don’t really see how a padlock would work in those holes. How would it prevent that deal from being turned up?

I also noticed that they don’t show her closing the deadbolt but it does appear she has already done so. However, they also show her hurriedly jamming in the pin on the lower latch that she was struggling with before she got it open, as though that was the necessary move to keep him locked in. That doesn’t appear to be the case if the deadbolt is already set, and it does also once again raise the question of why you would have that pin at all. Are you sure that’s not the place the padlock would go?

We are talking past each other. You are talking about its function in the plot and I am talking about the realism of a door like that existing in a hotel or really anywhere. Despite the supernatural elements, most everything physical we see otherwise is realistic.

It's left ambiguous and interpretable, but (I think) only to the extent that Kubrick is forcing us to make rationalizations for what happened - exactly as Jack and Wendy are doing concerning Danny and the abuse. Jack even denies he saw anything in Room 237 when we know he did (or at least thought he did). He's giving the audience an (cop)out for not accepting how the door was opened. I feel that's the reason why the door lock system is so bizarre and seemingly unnecessary and why Kubrick draws so much attention to it.

I think his statements about the "God concept" in an interview about 2001 are very revealing about what his intentions were. It's not just that one interview about The Shining. I am NOT saying Kubrick believed in God, but that he was open-minded about certain things that haven't been explained yet by our current level of science and perception as humans. This phone interview with the Japanese "paranormal investigator" in this video further bolsters the idea that Kubrick took this seriously: https://youtu.be/fVlXbS0SNqk

Kubrick on ESP: "I'd be surprised if it was true. I'd be surprised if it wasn't true."