linux-kernel - Hazard pointer enabled refcount prototype

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Message-ID: <3b749585-1286-4a4e-acd0-1534b60172da@efficios.com>
Date: Fri, 4 Oct 2024 15:52:01 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Boqun Feng <boqun.feng@...il.com>, paulmck <paulmck@...nel.org>,
 linux-kernel <linux-kernel@...r.kernel.org>
Subject: Hazard pointer enabled refcount prototype

Hi Greg,

After our discussion at KR2024, I've created a prototype adding hazard pointer
dereference support to refcount.h:

https://github.com/compudj/linux-dev/commit/234523dc9be90f1bc9221bf2d430c9187ac61528

Branch: https://github.com/compudj/linux-dev/tree/hp-6.11-refcount

It allows dereferencing a pointer to a refcount and incrementing the refcount,
without relying on RCU.

A good candidate for this would be the "usblp" driver which is using a static mutex
for existence guarantees. Introducing a refcount as first field of struct usblp
should do the trick.

I am not entirely sure if this kind of use-case justifies introducing hazard pointers
though, as this can be done just as well with RCU. I'll let you be the judge on this.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com