linux-kernel - Re: [RFC PATCH v5 1/2] fuse: new work queue to periodically invalidate expired dentries

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <87ldmukzff.fsf@wotan.olymp>
Date: Thu, 04 Sep 2025 16:30:44 +0100
From: Luis Henriques <luis@...lia.com>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: Bernd Schubert <bernd@...ernd.com>,  Laura Promberger
 <laura.promberger@...n.ch>,  Dave Chinner <david@...morbit.com>,  Matt
 Harvey <mharvey@...ptrading.com>,  linux-fsdevel@...r.kernel.org,
  kernel-dev@...lia.com,  linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v5 1/2] fuse: new work queue to periodically
 invalidate expired dentries

On Thu, Sep 04 2025, Miklos Szeredi wrote:

> On Thu, 4 Sept 2025 at 16:00, Luis Henriques <luis@...lia.com> wrote:
>>
>> Hi Miklos,
>>
>> On Thu, Sep 04 2025, Miklos Szeredi wrote:
>>
>> > On Thu, 28 Aug 2025 at 18:30, Luis Henriques <luis@...lia.com> wrote:
>
>> >> +       if (!inval_wq && RB_EMPTY_NODE(&fd->node))
>> >> +               return;
>> >
>> > inval_wq can change to zero, which shouldn't prevent removing from the rbtree.
>>
>> Maybe I didn't understood your comment, but isn't that what's happening
>> here?  If the 'fd' is in a tree, it will be removed, independently of the
>> 'inval_wq' value.
>
> I somehow thought it was || not &&.
>
> But I still don't see the point.  The only caller already checked
> RB_EMPTY_NODE, so that is false. No race possible since it's called
> form the destruction of the dentry, and so this expression is
> guaranteed to evaluate to false.

Fair enough.  I'll drop that code.

>> (By the way, I considered using mutexes here instead.  Do you have any
>> thoughts on this?)
>
> Use mutex where protected code might sleep, spin lock otherwise.
>
>>
>> What I don't understand in your comment is where you suggest these helpers
>> could be in a higher level.  Could you elaborate on what exactly you have
>> in mind?
>
> E.g.
>
> void d_dispose_if_unused(struct dentry *dentry, struct list_head *dispose)
> {
>         spin_lock(&dentry->d_lock);
>         if (!dentry->d_lockref.count)
>                 to_shrink_list(dentry, dispose);
>         spin_unlock(&dentry->d_lock);
> }
>
> Which is in fact taken from d_prune_aliases(), which could be modified
> to use this helper.

Oh! OK, got it.  Thanks, I'll start working on v6 and try to include all
your suggestions.

Cheers,
-- 
Luís