linux-kernel - Re: [PATCH v4 08/35] locking/rwlock, spinlock: Support Clang's context analysis

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251211114905.GE3911114@noisy.programming.kicks-ass.net>
Date: Thu, 11 Dec 2025 12:49:05 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Marco Elver <elver@...gle.com>
Cc: Boqun Feng <boqun.feng@...il.com>, Ingo Molnar <mingo@...nel.org>,
	Will Deacon <will@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
	Chris Li <sparse@...isli.org>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Alexander Potapenko <glider@...gle.com>,
	Arnd Bergmann <arnd@...db.de>, Bart Van Assche <bvanassche@....org>,
	Christoph Hellwig <hch@....de>, Dmitry Vyukov <dvyukov@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Frederic Weisbecker <frederic@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Ian Rogers <irogers@...gle.com>, Jann Horn <jannh@...gle.com>,
	Joel Fernandes <joelagnelf@...dia.com>,
	Johannes Berg <johannes.berg@...el.com>,
	Jonathan Corbet <corbet@....net>,
	Josh Triplett <josh@...htriplett.org>,
	Justin Stitt <justinstitt@...gle.com>, Kees Cook <kees@...nel.org>,
	Kentaro Takeda <takedakn@...data.co.jp>,
	Lukas Bulwahn <lukas.bulwahn@...il.com>,
	Mark Rutland <mark.rutland@....com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Thomas Gleixner <tglx@...utronix.de>, Thomas Graf <tgraf@...g.ch>,
	Uladzislau Rezki <urezki@...il.com>,
	Waiman Long <longman@...hat.com>, kasan-dev@...glegroups.com,
	linux-crypto@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-security-module@...r.kernel.org,
	linux-sparse@...r.kernel.org, linux-wireless@...r.kernel.org,
	llvm@...ts.linux.dev, rcu@...r.kernel.org
Subject: Re: [PATCH v4 08/35] locking/rwlock, spinlock: Support Clang's
 context analysis

On Thu, Nov 20, 2025 at 04:09:33PM +0100, Marco Elver wrote:

> To avoid warnings in constructors, the initialization functions mark a
> lock as acquired when initialized before guarded variables.

> diff --git a/include/linux/rwlock.h b/include/linux/rwlock.h
> index 5b87c6f4a243..a2f85a0356c4 100644
> --- a/include/linux/rwlock.h
> +++ b/include/linux/rwlock.h
> @@ -22,23 +22,24 @@ do {								\
>  	static struct lock_class_key __key;			\
>  								\
>  	__rwlock_init((lock), #lock, &__key);			\
> +	__assume_ctx_guard(lock);				\
>  } while (0)
>  #else
>  # define rwlock_init(lock)					\
> -	do { *(lock) = __RW_LOCK_UNLOCKED(lock); } while (0)
> +	do { *(lock) = __RW_LOCK_UNLOCKED(lock); __assume_ctx_guard(lock); } while (0)
>  #endif

This is again somewhat magical and confused the living daylight out of
me. I know (from having looked back on previous discussions) that I was
confused about this before, and clearly it didn't stick.

So obviously I'll be confused again when I look at this code in a years
time or so :/

Can we get a comment near this __assume_ctx_guard() thing (because
putting it all over the lock initializers would probably be duplicating
things too much)?