Smoke on the Water is a mixture of minor modes.
The main riff has phrygian and even locrian elements:
Code:
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0---3---5-----0---3---6--5------
0---3---5-----0---3---6--5------
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R b3 4 R b3 b5 4
5 b7 R 5 b7 b2 R
There's a phrygian b2, but both kinds of 5th (perfect, and the locrian or blues b5).
But the chorus starts with a C major chord, which is a IV chord in G dorian. (The vocal melody is a strong E natural over the C, the dorian 6th of G.)
But then they follow the C with Ab, which is a bII back in G phrygian (and resolves back to Gm).
So the best you can say (IMO) is it's "in G minor", but with plenty of parallel modal borrowing.