Re: [PATCH v3 2/3] prandom: Convert prandom_u32_state() to __always_inline

From: David Laight <david.laight.linux@gmail.com>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Huacai Chen <chenhuacai@kernel.org>,
	Madhavan Srinivasan <maddy@linux.ibm.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Alexander Gordeev <agordeev@linux.ibm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Kees Cook <kees@kernel.org>,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Mark Rutland <mark.rutland@arm.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Jeremy Linton <jeremy.linton@arm.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev,
	linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
	linux-s390@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH v3 2/3] prandom: Convert prandom_u32_state() to __always_inline
Date: Fri, 2 Jan 2026 22:54:03 +0000	[thread overview]
Message-ID: <20260102225403.78e26214@pumpkin> (raw)
In-Reply-To: <CAHmME9qHiVZwf4TAringRHSZ-yqHuPwmP=Wnx98n09jv7Vu_Rg@mail.gmail.com>

On Fri, 2 Jan 2026 14:39:21 +0100
"Jason A. Donenfeld" <Jason@zx2c4.com> wrote:

> Hi Ryan,
...
> > +static __always_inline u32 prandom_u32_state(struct rnd_state *state)  
> 
> Why not just normal `inline`? Is gcc disagreeing with the inlinability
> of this function?

gcc has a mind of its own when it comes to inlining.
If there weren't some massive functions marked 'inline' that should never
really be inlined then making 'inline' '__always_inline' would make sense.
But first an audit would be needed.
(This has come up several times in the past.)
But if you need a function to be inlined (for any reason) it needs to be
always_inline.

Whether there should be an non-inlined 'option' here is another matter.
There could be a normal function that calls the inlined version.

	David

> 
> Jason
> 