I'm currently writing a journal article to be published, and the work from this article is basically the entire work of my Master's thesis. 

Clearly a thesis is usually more involved and fleshed out than a journal article, but how much direct copying is usually permitted? Is it okay to directly copy-and-paste an entire chapter (or multiple chapters) of this article into my thesis, given that I wrote it anyway? At what point am I plagiarising myself?