If you want another way to do this, you can use Icicles. A non-negative prefix arg with command
C-c ') searches multiple buffers line by line (like
grep). If you hit
C-! at the prompt that asks which buffers then all buffers are searched.
C-9 C-c ' C-! RET
C-9 says search multiple buffers.
C-c ' is
icicle-occur, which is a line-by-line search, like
C-! says choose all candidates (the candidates are the existing buffers).
RET ends choosing buffers.
Then you type whatever search patterns you want. The search hits are shown in popup buffer
*Completions*. Change your minibuffer input and the matching hits change. Use
S-SPC to lock in one pattern and add an additional pattern to match. You can use
down to cycle among candidates or continue to narrow the choices. You can cycle showing the matches in context in the buffers, using
Each search candidate is a buffer line followed by the buffer name. You can match both if you like. Matching can be using any number of search patterns (separated using
S-SPC), and each pattern can be a regexp (or other kinds of patterns).