As you may be aware, starting with 4.12-rc1 Linus will no longer provide signed tarballs and patches for pre-release ("-rc") kernels. Reasons for this are multiple, but largely this is because people who are most interested in pre-release tags -- kernel developers -- do not rely on patches and tarballs to do their work.
Obtaining tarballs on your own
Here is how you can generate the tarball from a pre-release tag using the "git archive" command (we'll use 4.12-rc1 in these examples):
git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git cd linux git verify-tag v4.12-rc1 git archive --format=tar.gz --prefix=linux-4.12-rc1/ \ -o linux-4.12-rc1.tar.gz v4.12-rc1
The upside of this method is that during the "git verify-tag" step you will check the PGP signature on the tag to make sure that what you cloned is exactly the same tree as on Linus Torvalds's computer.
The downside of this method is that you will need to download about 1 GiB of data -- the entire git history of the Linux kernel -- just to get the latest tag. Notably, when -rc2 is tagged, all you'll need to do is run a quick "git pull" to get the latest objects and it will be dramatically less data to download, so cloning the whole tree may be worth it to you in the long run if you plan to do this again in the future.
If you do not want to download the whole git repository and just want to get the latest tarball, you can download the version automatically generated by cgit at the following (or similar URL):
Please note that you will not be able to cryptographically verify the integrity of this archive, but the download will be about 10 times less in size than the full git tree.
Obtaining patches to the previous mainline
If you would like to get just the patch to the previous mainline release, you can get it from cgit as well:
wget -O patch-4.12-rc1 https://git.kernel.org/torvalds/p/v4.12-rc1/v4.11
Unfortunately, cgit does not currently offer an easy way to get gzip-compressed patches, but if you would like to reduce the amount of data you download, you can use http-level gzip compression:
wget -O patch-4.12-rc1.gz --header="accept-encoding: gzip" \ https://git.kernel.org/torvalds/p/v4.12-rc1/v4.11
The links to these patches are available on the front page of https://www.kernel.org/.
Why not provide these at their old locations?
We intentionally did not provide these automatically generated tarballs and patches in locations previously used by Linus (/pub/linux/kernel/v4.x/testing), even if this meant potentially breaking automated scripts relying on contents published there. Anything placed in the /pub tree is signed and curated directly by developers and all patches and software archives published there invariably come with a PGP signature provided directly by the developer of that software (or one of the developers).
Patches and tarballs automatically generated by git.kernel.org are NOT a replacement for this stringent process, but merely a convenience service that comes with very different trust implications. By providing these at different URLs we wanted all users of these services to make a conscious decision on whether they want to trust these automatically generated tarballs and patches, or whether they want to change their process to continue to use PGP-verifiable tags directly from the git tree.