Re: ipv4/tcp.c:4234:1: error: the frame size of 1152 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]

From: Nathan Chancellor <nathan@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>,
	Naresh Kamboju <naresh.kamboju@linaro.org>,
	Mathias Nyman <mathias.nyman@intel.com>,
	Johannes Berg <johannes@sipsolutions.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Shuah Khan <skhan@linuxfoundation.org>,
	Brendan Higgins <brendanhiggins@google.com>,
	Ariel Elior <aelior@marvell.com>,
	GR-everest-linux-l2@marvell.com, Wei Liu <wei.liu@kernel.org>
Cc: Linux ARM <linux-arm-kernel@lists.infradead.org>,
	open list <linux-kernel@vger.kernel.org>,
	Netdev <netdev@vger.kernel.org>,
	lkft-triage@lists.linaro.org, Arnd Bergmann <arnd@arndb.de>,
	"David S. Miller" <davem@davemloft.net>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Alexei Starovoitov <ast@kernel.org>,
	Eric Dumazet <edumazet@google.com>
Subject: Re: ipv4/tcp.c:4234:1: error: the frame size of 1152 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
Date: Tue, 7 Sep 2021 16:35:26 -0700	[thread overview]
Message-ID: <92c20b62-c4a7-8e63-4a94-76bdf6d9481e@kernel.org> (raw)
In-Reply-To: <CAHk-=whF9F89vsfH8E9TGc0tZA-yhzi2Di8wOtquNB5vRkFX5w@mail.gmail.com>

On 9/7/2021 4:14 PM, Linus Torvalds wrote:
> There are many more of these cases. I've seen Hyper-V allocate 'struct
> cpumask' on the stack, which is once again an absolute no-no that
> people have apparently just ignored the warning for. When you have
> NR_CPUS being the maximum of 8k, those bits add up, and a single
> cpumask is 1kB in size. Which is why you should never do that on
> stack, and instead use '
> 
>         cpumask_var_t mask;
>         alloc_cpumask_var(&mask,..)
> 
> which will do a much more reasonable job. But the reason I call out
> hyperv is that as far as I know, hyperv itself doesn't actually
> support 8192 CPU's. So all that apic noise with 'struct cpumask' that
> uses 1kB of data when NR_CPUS is set to 8192 is just wasted. Maybe I'm
> wrong. Adding hyperv people to the cc too.

I am only commenting on this because I was looking into an instance of 
this warning yesterday with Fedora's arm64 config, which has 
CONFIG_NR_CPUS=4096:

https://lore.kernel.org/r/YTZyMx91zV9kfDkQ@Ryzen-9-3900X.localdomain/

Won't your example only fix the issue with CONFIG_CPUMASK_OFFSTACK=y or 
am I misreading the gigantic comment in include/linux/cpumask.h? As far 
as I can tell, only x86 selects it and it is not user configurable 
unless CONFIG_DEBUG_PER_CPU_MAPS is set, which is buried in the debug 
options so most people won't bother trying to enable it. If I understand 
correctly, how should these be dealt with in the case of 
CONFIG_CPUMASK_OFFSTACK=n?

Cheers,
Nathan