On Wed, Jan 01, 2014 at 01:37:46PM +0100, Gerhard Sittig wrote:

Last time I checked (few days ago, 'git grep -w Fixes:') it
wasn't, at least not within the kernel source tree and its
Documentation hierarchy.  Today's master still does not have it.

But a quick search in recent LAKML messages reveals that it's
been in use by e.g. Olof Johansson, Jason Cooper, Rusty Russell,
Dan Carpenter, Russell King, Mark Brown, Stephen Warren, Paul
Walmsley, and I'm not making this up but am just referring to
what repeatedly was requested in the past.  The form used there
was "Fixes: <hash> (<oneline>)" though.  A doc update may be due
to have a canonical format.

It was discussed at kernel summit, and I believe the resulting format
was only published in one of the kernel summit mailing lists.  The
outcome of it as I understand was that the format is:

Fixes: <hash> ("<one line summary>")

Though the addition of the quotes was (iirc) only something added after
the vocal discussion.  If you mail Linus a patch with a fixes line which
doesn't match that, Linus will probably fix it up... (Linus has done that
with one of mine in the past.)