linux-kernel - Re: [Patch, RFC] Make struct fb

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

Date:	Tue, 21 Sep 2010 07:56:10 +0200
From:	Bruno Prémont <bonbons@...ux-vserver.org>
To:	Florian Tobias Schandinat <FlorianSchandinat@....de>
Cc:	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Bernie Thompson <bernie@...gable.com>
Subject: Re: [Patch, RFC] Make struct fb_info ref-counted with kref

On Tue, 21 Sep 2010 00:28:27 Florian Tobias Schandinat <FlorianSchandinat@....de> wrote:
> > Tracking if/how often framebuffer is opened as such is a separate thing (though
> > all users that have the framebuffer opened hold a reference to fb_info).
> 
> That's what I said. So as long as refcount <= 1 it does not matter whether you 
> just count on open/release or additionally on every framebuffer operation, just 
> that the later produces more noise.

Hm, I don't count on every framebuffer operation... in most cases
fb_info is provided as function argument, in which case no further
counting is needed as the caller has a valid reference.

With my patch applied refcount for registered but unsed framebuffer was
2 (once for the driver, once for registered_fb entry) and went up to 3
when userspace opened framebuffer. fbcon's usage only incremented
refcount for very short timeframes when effectively using fb_info.

When starting with the FB minor I have to take a new reference.
(though I maybe should check if file's private data is set and use
that reference instead of looking up fb_info by minor as is currently
done)

For fbcon all the references are taken by FB minor (I wondered why
fbcon only remembers index into registered_fb aka minor instead of
fb_info itself)

> So I still don't see any advantage in counting users + uses.
> Please note that I do not object the idea of the patch itself, it's only that I 
> have a different preference on what to count. I only want to express that your 
> way is more complicated than what I would recommend.

I don't think I see how you would do the refcounting... would you just
drop the changes in fb_open() and fb_release()?
Could you describe your approach (with pseudo-code) or the differences
to mine?

Thanks,
Bruno

> But if you want to go on I do not object. As long as the end result works that's 
> okay with me.
> 
> 
> Thanks
> 
> Florian Tobias Schandinat
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/