Alan Cox provides an explanation of how Linux kernel patches are
handled in this edition of Ask Slashdot:
"Probably the first thing to explain is the Red Hat
kernel. That actually isn't something I am responsible for. Arjan
van de Ven is the keeper of the distribution kernel, and has the
unenviable task of getting a kernel together that will actually
pass all the brutal QA testing. Arjan is perfectly entitled to (and
sometimes does) throw out bits of -ac changes.
You'll see Red Hat patches being merged into -ac and Linus trees
when appropriate, often from Arjan or Pete Zaitcev. Many of the
other patches in the RH tree are considered "fixups" - they are
workarounds for problems but not generalised or clean enough to
feed into the main tree without further work. Others are RH
specific patches for things like packaging.
With the -ac tree I try and do rapid rolling releases, sucking
in new code to test it and also its interactions with other new
code. By doing releases every few days I get a high number of
people testing and reporting bugs before there are too many
possible causes. This is how Linus trees used to work long ago, and
I still think its the better technique."