Re: [GIT PULL] Second batch of KVM changes for Linux 5.6-rc4 (or rc5)

On 01/03/20 22:33, Linus Torvalds wrote:

On Sun, Mar 1, 2020 at 1:03 PM Paolo Bonzini [off-list ref] wrote:

quoted

Paolo Bonzini (4):
      KVM: allow disabling -Werror

Honestly, this is just badly done.

You've basically made it enable -Werror only for very random
configurations - and apparently the one you test.
Doing things like COMPILE_TEST disables it, but so does not having
EXPERT enabled.

Yes, I took this from the i915 Kconfig.  It's temporary, in 5.7 I am
planning to get it to just !KASAN, but for 5.6 I wanted to avoid more
breakage so I added the other restrictions.  The difference between
x86-64 and i386 is really just the frame size warnings, which Christoph
triggered because of a higher CONFIG_NR_CPUS.

(BTW, perhaps it makes sense for Sparse to have something like __nostack
for structs that contain potentially large arrays).

I've merged this, but I wonder why you couldn't just do what I
suggested originally?  Seriously, if you script your build tests,
and don't even look at the results, then you might as well use

   make KCFLAGS=-Werror

I did that and I'm also adding W=1; and I threw in a smaller than
default frame size warning option too because I don't want cpumasks on
the stack anyway.  However, that wouldn't help contributors.  I'm okay
if I get W=1 or frame size warnings from patches from other
contributors, but I think it's a disservice to them that they have to
set KCFLAGS in order to avoid warnings.

the "now it causes problems for
random compiler versions" is a real issue again - but at least it
wouldn't be a random kernel subsystem that happens to trigger it, it
would be a _generic_ issue, and we'd have everybody involved when a
compiler change introduces a new warning.

Yes, and GCC prereleases are tested with Linux, for example by doing
full Rawhide rebuilds.  If we started using -Werror by default
(including allyesconfig), they would probably report warnings early.
Same for clang.

I hope that Linux can have -Werror everywhere, or at least a
CONFIG_WERROR option that does it even if it defaults to n for a release
or more.  But I don't think we can get there without first seeing what
issues pop up in a few subsystems or arches---even before considering
new compilers---so I decided I would just try.

Paolo

Adding the powerpc people, since they have more history with their
somewhat less hacky one. Except that one automatically gets disabled
by "make allmodconfig" and friends, which is also kind of pointless.

Michael, what tends to be the triggers for people using
PPC_DISABLE_WERROR? Do you have reports for it? Could we have a
_generic_ option that just gets enabled by default, except it gets
disabled by _known_ issues (like KASAN).

Being disabled for "make allmodconfig" is kind of against one of the
_points_ of "the build should be warning-free".