Lawrence D'Oliveiro
Email: <ldo AT SPAMFREE geek-central DOT gen DOT nz>
Invaluable resource for browsing the Linux sources: Visit http://lxr.linux.no/. (I can't seem to get text searching to work, but see below for a tip for that.)
Quickly list all source files mentioning a particular identifier:
find /usr/src/linux/ -name '*.[chS]' -exec grep -q identifier '{}' ';' -print
Then it's easy enough to pull up the appropriate source file as http://lxr.linux.no/source/path.