linux-kernel - Re: [patch 2/2] Documentation/process: Add tip tree handbook

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Message-ID: <alpine.DEB.2.21.1811071842340.1906@nanos.tec.linutronix.de>
Date:   Wed, 7 Nov 2018 18:44:07 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
cc:     x86@...nel.org, Peter Zijlstra <peterz@...radead.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        John Stultz <john.stultz@...aro.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Andy Lutomirski <luto@...nel.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Mark Brown <broonie@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [patch 2/2] Documentation/process: Add tip tree handbook

On Wed, 7 Nov 2018, Thomas Gleixner wrote:

> Add a document to the subsystem/maintainer handbook section, which explains
> what the tip tree is, how it operates and what rules and expectations it
> has.

Peter asked me to add a section about locking comments. I added it and
forgot to refresh the patch before sending. Delta patch below.

Thanks,

	tglx
---
--- a/Documentation/process/maintainer-tip.rst
+++ b/Documentation/process/maintainer-tip.rst
@@ -578,6 +578,29 @@ Sentences in comments start with a upper
   usage of descriptive function names often replaces these tiny comments.
   Apply common sense as always.
 
+ 
+Documenting locking requirements
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  Documenting locking requirements is a good thing, but comments are not
+  necessarily the best choice. Instead of writing::
+
+    	/* Caller must hold foo->lock */
+	void func(struct foo *foo)
+	{
+		...
+	}
+
+  Please use::
+
+	void func(struct foo *foo)
+	{
+		lockdep_assert_held(&foo->lock);
+		...
+	}
+
+  The latter enables run time debugging when lockdep is enabled which
+  verifies that all callers hold the lock. Comments can't do that.
+
 
 Bracket rules
 ^^^^^^^^^^^^^