linux-kernel - Re: Documentation of locking needs when working with lists?

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Message-ID: <2025051012-karma-setting-af04@gregkh>
Date: Sat, 10 May 2025 15:20:47 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Heiner Kallweit <hkallweit1@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Documentation of locking needs when working with lists?

On Sat, May 10, 2025 at 10:46:32AM +0200, Heiner Kallweit wrote:
> Even though lists are used everywhere, I was surprised not being able to find
> documentation about which operations need locking, and which ones are safe
> lock-less.
> 
> My case:
> I have a list where the only operation is adding entries.
> It's clear that adding entries has to be serialized.
> Question is whether a list_for_each_entry is safe lock-less.
> 
> Looking at the code I *think* it's safe, under the precondition that
> reading/writing pointers is atomic.
> 
> Any hint or documentation link would be appreciated. Thanks!

You MUST have locking for your list if you have multiple processes
accessing it at the same time.

good luck!

greg k-h