linux-kernel - Re: [PATCH v3] driver core: fw_devlink: Stop trying to optimize cycle detection logic

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Message-ID: <CAMuHMdWv+x31-3OaKFKHJHJwK+KB0Hi3yJMRUJ3rqEThY=EE7Q@mail.gmail.com>
Date: Tue, 19 Nov 2024 14:40:25 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Saravana Kannan <saravanak@...gle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Francesco <francesco.dolcini@...adex.com>, 
	Tomi Valkeinen <tomi.valkeinen@...asonboard.com>, kernel-team@...roid.com, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] driver core: fw_devlink: Stop trying to optimize cycle
 detection logic

Hi Saravana,

On Wed, Oct 30, 2024 at 6:10 PM Saravana Kannan <saravanak@...gle.com> wrote:
> In attempting to optimize fw_devlink runtime, I introduced numerous cycle
> detection bugs by foregoing cycle detection logic under specific
> conditions. Each fix has further narrowed the conditions for optimization.
>
> It's time to give up on these optimization attempts and just run the cycle
> detection logic every time fw_devlink tries to create a device link.
>
> The specific bug report that triggered this fix involved a supplier fwnode
> that never gets a device created for it. Instead, the supplier fwnode is
> represented by the device that corresponds to an ancestor fwnode.
>
> In this case, fw_devlink didn't do any cycle detection because the cycle
> detection logic is only run when a device link is created between the
> devices that correspond to the actual consumer and supplier fwnodes.
>
> With this change, fw_devlink will run cycle detection logic even when
> creating SYNC_STATE_ONLY proxy device links from a device that is an
> ancestor of a consumer fwnode.
>
> Reported-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
> Closes: https://lore.kernel.org/all/1a1ab663-d068-40fb-8c94-f0715403d276@ideasonboard.com/
> Fixes: 6442d79d880c ("driver core: fw_devlink: Improve detection of overlapping cycles")
> Tested-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
> Signed-off-by: Saravana Kannan <saravanak@...gle.com>

Thanks for your patch, which is now commit bac3b10b78e54b7d ("driver
core: fw_devlink: Stop trying to optimize cycle detection logic") in
next-20241107 and later.

> Geert/Francesco,
>
> If you want to test this patch, pull it in and compare the output of
> the following:
>
> ls -1 /sys/class/devlink
>
> The only device links that should be missing with the patch should be
> device links in a cycle that weren't detected before.

I gave it a try on all my boards, and compared the output on a few of
them, and everything looks fine.

Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds