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From: John Ogness <john.ogness@linutronix.de>
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To: Petr Mladek <pmladek@suse.com>
Cc: "Rob Herring (Arm)" <robh@kernel.org>, Linus Torvalds
 <torvalds@linux-foundation.org>, Steven Rostedt <rostedt@goodmis.org>,
 Andy Shevchenko <andriy.shevchenko@linux.intel.com>, Rasmus Villemoes
 <linux@rasmusvillemoes.dk>, Sergey Senozhatsky <senozhatsky@chromium.org>,
 Jonathan Corbet <corbet@lwn.net>, Saravana Kannan <saravanak@google.com>,
 Andrew Morton <akpm@linux-foundation.org>, Peter Zijlstra
 <peterz@infradead.org>, Thomas Gleixner <tglx@linutronix.de>, Zijun Hu
 <quic_zijuhu@quicinc.com>, linux-doc@vger.kernel.org,
 linux-kernel@vger.kernel.org, devicetree@vger.kernel.org
Subject: Re: lock in vsprintf(): was: Re: [PATCH] of: Add printf '%pOFm' for
 generating modalias
In-Reply-To: <Z2Q2TcM6QPUIIyLC@pathway.suse.cz>
References: <20241217183711.2525863-1-robh@kernel.org>
 <Z2K_u6jK5aLDqaam@pathway.suse.cz> <84wmfxm6em.fsf@jogness.linutronix.de>
 <Z2Q2TcM6QPUIIyLC@pathway.suse.cz>
Date: Thu, 19 Dec 2024 20:17:21 +0106
Message-ID: <84o7171o9y.fsf@jogness.linutronix.de>
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On 2024-12-19, Petr Mladek <pmladek@suse.com> wrote:
> I do not want to revert everything now just because of theoretical
> problems.

What would you revert? This has always been an issue for printk().

> Well, it would be nice to document the lock dependency in
> Documentation/core-api/printk-formats.rst

Yes. If any locking is involved at all, such specifiers should be
documented as not safe in NMI context or within printk_cpu_sync
blocks. Also, it should be checked if all such locks are
raw_spinlock_t. If any other lock type is used, it probably is already
generating a lockdep splat since printk() formats records with local
interrupts off.

Perhaps we should create a kunit that calls printk() for each of the
supported specifiers and see if any lockdep splats appear.

John