If, rather than a documentation bug, you think you've found a bug in a system call (i.e., in the Linux kernel), or in a library function (i.e., in glibc), then look here.
The way to report a man-pages bug depends on the type of bug:
mtk.manpages-AT-gmail.comPlease do not report such bugs to the mailing list, or via the bugzilla. Doing so creates unnecessary noise on the list and unnecessary bugzilla administrative overhead.
You will need to create an account on this bugzilla if you don't already have one. This bugzilla is oriented towards Linux kernel bugs, so includes template text that is not relevant for most man-pages bug reports. Don't worry about reporting the Tree, Alias, or Kernel Version (just specify "n/a"), and you can ignore the template text under Description.
Want to report a bug for a man page that belongs to a package other than man-pages? Look here.