linux-kernel - Re: [PATCH RFC 3/4] lockref: rework CMPXCHG

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Message-ID: <20240805-unser-viren-4f1860143b6e@brauner>
Date: Mon, 5 Aug 2024 13:44:40 +0200
From: Christian Brauner <brauner@...nel.org>
To: Jeff Layton <jlayton@...nel.org>
Cc: Mateusz Guzik <mjguzik@...il.com>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, 
	Andrew Morton <akpm@...ux-foundation.org>, Josef Bacik <josef@...icpanda.com>, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 3/4] lockref: rework CMPXCHG_LOOP to handle
 contention better

> Audit not my favorite area of the kernel to work in either. I don't see
> a good way to make it rcu-friendly, but I haven't looked too hard yet
> either. It would be nice to be able to do some of the auditing under
> rcu or spinlock.

For audit your main option is to dodge the problem and check whether
audit is active and only drop out of rcu if it is. That sidesteps the
problem. I'm somewhat certain that a lot of systems don't really have
audit active.

>From a brief look at audit it would be quite involved to make it work
just under rcu. Not just because it does various allocation but it also
reads fscaps from disk and so on. That's not going to work unless we add
a vfs based fscaps cache similar to what we do for acls. I find that
very unlikely.