linux-kernel - Re: [PATCH RFC 11/24] locking/mutex: Support Clang's capability analysis

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Message-ID: <38bde2a3-762d-49ed-a2a6-ac3bd698bedc@acm.org>
Date: Fri, 7 Feb 2025 12:58:20 -0800
From: Bart Van Assche <bvanassche@....org>
To: Peter Zijlstra <peterz@...radead.org>, Marco Elver <elver@...gle.com>
Cc: "Paul E. McKenney" <paulmck@...nel.org>,
 Alexander Potapenko <glider@...gle.com>, Bill Wendling <morbo@...gle.com>,
 Boqun Feng <boqun.feng@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>,
 Frederic Weisbecker <frederic@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Ingo Molnar <mingo@...nel.org>, Jann Horn <jannh@...gle.com>,
 Joel Fernandes <joel@...lfernandes.org>, Jonathan Corbet <corbet@....net>,
 Josh Triplett <josh@...htriplett.org>, Justin Stitt
 <justinstitt@...gle.com>, Kees Cook <kees@...nel.org>,
 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 <ndesaulniers@...gle.com>,
 Steven Rostedt <rostedt@...dmis.org>, Thomas Gleixner <tglx@...utronix.de>,
 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
Subject: Re: [PATCH RFC 11/24] locking/mutex: Support Clang's capability
 analysis

On 2/7/25 12:31 AM, Peter Zijlstra wrote:
> Can we please fix up all the existing __cond_lock() code too?

It would be great to get rid of __cond_lock().

In the description of commit 4a557a5d1a61 ("sparse: introduce
conditional lock acquire function attribute") I found the following
URL: 
https://lore.kernel.org/all/CAHk-=wjZfO9hGqJ2_hGQG3U_XzSh9_XaXze=HgPdvJbgrvASfA@mail.gmail.com/

That URL points at an e-mail from Linus Torvalds with a patch for sparse
that implements support for __cond_acquires(). It seems to me that the
sparse patch has never been applied to the sparse code base (the git URL
for sparse is available at https://sparse.docs.kernel.org/en/latest/).
Additionally, the most recent commit to the sparse code base is from
more than a year ago (see also 
https://git.kernel.org/pub/scm/devel/sparse/sparse.git/).

In other words, switching from __cond_lock() to __cond_acquires()
probably will make sparse report more "context imbalance" warnings.

If this is a concern to anyone, please speak up.

Thanks,

Bart.