From: Al Viro <viro@zeniv.linux.org.uk>
To: NeilBrown <neil@brown.name>
Cc: Kees Cook <kees@kernel.org>,
Joel Granados <joel.granados@kernel.org>,
linux-fsdevel@vger.kernel.org,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3?] proc_sysctl: remove rcu_dereference() for accessing ->sysctl
Date: Fri, 4 Jul 2025 03:03:48 +0100 [thread overview]
Message-ID: <20250704020348.GN1880847@ZenIV> (raw)
In-Reply-To: <175159315670.565058.128329102948224076@noble.neil.brown.name>
On Fri, Jul 04, 2025 at 11:39:16AM +1000, NeilBrown wrote:
> On Fri, 04 Jul 2025, Al Viro wrote:
> > On Mon, Jun 16, 2025 at 12:49:51PM +1000, NeilBrown wrote:
> >
> > > The reality is that ->sysctl does not need rcu protection. There is no
> > > concurrent update except that it can be set to NULL which is pointless.
> >
> > I would rather *not* leave a dangling pointer there, and yes, it can
> > end up being dangling. kfree_rcu() from inside the ->evict_inode()
> > may very well happen earlier than (also RCU-delayed) freeing of struct
> > inode itself.
>
> In that case could we move the proc_sys_evict_inode() call from
> proc_evict_inode() to proc_free_inode(), and replace kfree_rcu() with
> kfree()?
proc_free_inode() can be called from softirq context, so we'd need to
touch all sysctl_lock users for that. Definitely a larger patch that
way, if nothing else...
prev parent reply other threads:[~2025-07-04 2:03 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-06-15 23:00 [PATCH v3?] proc_sysctl: remove rcu_dereference() for accessing ->sysctl NeilBrown
2025-06-15 23:57 ` Al Viro
2025-06-16 2:49 ` NeilBrown
2025-07-03 23:43 ` Al Viro
2025-07-04 1:02 ` Al Viro
2025-07-04 1:39 ` NeilBrown
2025-07-04 2:19 ` Al Viro
2025-07-04 1:39 ` NeilBrown
2025-07-04 2:03 ` Al Viro [this message]
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