linux-kernel - Re: [PATCH v4 06/35] cleanup: Basic compatibility with context analysis

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Message-ID: <20251211095516.GO3707837@noisy.programming.kicks-ass.net>
Date: Thu, 11 Dec 2025 10:55:16 +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>,
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	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>,
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	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Thomas Gleixner <tglx@...utronix.de>, Thomas Graf <tgraf@...g.ch>,
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Subject: Re: [PATCH v4 06/35] cleanup: Basic compatibility with context
 analysis

On Thu, Nov 20, 2025 at 04:09:31PM +0100, Marco Elver wrote:
> Introduce basic compatibility with cleanup.h infrastructure: introduce
> DECLARE_LOCK_GUARD_*_ATTRS() helpers to add attributes to constructors
> and destructors respectively.
> 
> Note: Due to the scoped cleanup helpers used for lock guards wrapping
> acquire and release around their own constructors/destructors that store
> pointers to the passed locks in a separate struct, we currently cannot
> accurately annotate *destructors* which lock was released. While it's
> possible to annotate the constructor to say which lock was acquired,
> that alone would result in false positives claiming the lock was not
> released on function return.
> 
> Instead, to avoid false positives, we can claim that the constructor
> "assumes" that the taken lock is held via __assumes_ctx_guard().
> 
> This will ensure we can still benefit from the analysis where scoped
> guards are used to protect access to guarded variables, while avoiding
> false positives. The only downside are false negatives where we might
> accidentally lock the same lock again:
> 
> 	raw_spin_lock(&my_lock);
> 	...
> 	guard(raw_spinlock)(&my_lock);  // no warning
> 
> Arguably, lockdep will immediately catch issues like this.
> 
> While Clang's analysis supports scoped guards in C++ [1], there's no way
> to apply this to C right now. Better support for Linux's scoped guard
> design could be added in future if deemed critical.

Moo, so the alias analysis didn't help here?