linux-kernel - Re: [PATCH v2] audit: Avoid excessive dput/dget in audit

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Message-ID: <20260205235351.GU3183987@ZenIV>
Date: Thu, 5 Feb 2026 23:53:51 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Waiman Long <llong@...hat.com>
Cc: Paul Moore <paul@...l-moore.com>, Eric Paris <eparis@...hat.com>,
	Christian Brauner <brauner@...nel.org>,
	linux-kernel@...r.kernel.org, audit@...r.kernel.org,
	Richard Guy Briggs <rgb@...hat.com>,
	Ricardo Robaina <rrobaina@...hat.com>
Subject: Re: [PATCH v2] audit: Avoid excessive dput/dget in audit_context
 setup and reset paths

On Wed, Feb 04, 2026 at 11:45:17PM -0500, Waiman Long wrote:

> @@ -70,6 +74,8 @@ void chroot_fs_refs(const struct path *old_root, const
> struct>
>                                 count++;
>                                 path_get(new_root);
>                         }
> +                       count += fs->pwd_xrefs;
> +                       fs->pwd_xrefs = 0;
>                         write_sequnlock(&fs->seq);

Nope - you only need that for threads that have ->pwd equal to old_root.
Incidentally, I'd forgotten about that sucker - it kills the idea of
fdget-like tricks dead, more's the pity.  Third-party modification of
task->fs->pwd (under task->lock and task->fs->seq), possible even with
task->fs->users == 1.

FWIW, I'm going through the fs_struct uses at the moment; will post
whatever I get when I go down (or earlier, in the unlikely case it doesn't
spill to tomorrow morning), will keep posting incremental followups
until the documentation is done.  I'm sick and tired of half-finished
docs - let's see if I can push through that one this way ;-/