linux-kernel - Re: [PATCH v2 00/34] Compiler-Based Capability- and Locking-Analysis

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Message-ID: <20250304112114.GE11590@noisy.programming.kicks-ass.net>
Date: Tue, 4 Mar 2025 12:21:14 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Marco Elver <elver@...gle.com>
Cc: "David S. Miller" <davem@...emloft.net>,
	Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Alexander Potapenko <glider@...gle.com>,
	Arnd Bergmann <arnd@...db.de>, Bart Van Assche <bvanassche@....org>,
	Bill Wendling <morbo@...gle.com>, Boqun Feng <boqun.feng@...il.com>,
	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>,
	Ingo Molnar <mingo@...nel.org>, Jann Horn <jannh@...gle.com>,
	Jiri Slaby <jirislaby@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Jonathan Corbet <corbet@....net>,
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	Mark Rutland <mark.rutland@....com>,
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	Nathan Chancellor <nathan@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
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	Uladzislau Rezki <urezki@...il.com>,
	Waiman Long <longman@...hat.com>, Will Deacon <will@...nel.org>,
	kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev, rcu@...r.kernel.org,
	linux-crypto@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH v2 00/34] Compiler-Based Capability- and Locking-Analysis

On Tue, Mar 04, 2025 at 10:20:59AM +0100, Marco Elver wrote:

> === Initial Uses ===
> 
> With this initial series, the following synchronization primitives are
> supported: `raw_spinlock_t`, `spinlock_t`, `rwlock_t`, `mutex`,
> `seqlock_t`, `bit_spinlock`, RCU, SRCU (`srcu_struct`), `rw_semaphore`,
> `local_lock_t`, `ww_mutex`.

Wasn't there a limitation wrt recursion -- specifically RCU is very much
a recursive lock and TS didn't really fancy that?


>   - Rename __var_guarded_by to simply __guarded_by. Initially the idea
>     was to be explicit about if the variable itself or the pointed-to
>     data is guarded, but in the long-term, making this shorter might be
>     better.
> 
>   - Likewise rename __ref_guarded_by to __pt_guarded_by.

Shorter is better :-)

Anyway; I think I would like to start talking about extensions for these
asap.

Notably I feel like we should have a means to annotate the rules for
access/read vs modify/write to a variable.

The obvious case is RCU; where holding RCU is sufficient to read, but
modification requires a 'real' lock. This is not something that can be
currently expressed.

The other is the lock pattern I touched upon the other day, where
reading is permitted when holding one of two locks, while writing
requires holding both locks.

Being able to explicitly write that in the __guarded_by() annotations is
the cleanest way I think.

Anyway, let me go stare at the actual patches :-)