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

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Message-ID: <2024110644-material-paternity-242f@gregkh>
Date: Wed, 6 Nov 2024 05:52:59 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Saravana Kannan <saravanak@...gle.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	Francesco <francesco.dolcini@...adex.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	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

On Tue, Nov 05, 2024 at 05:30:20PM -0800, Saravana Kannan wrote:
> On Wed, Oct 30, 2024 at 10:10 AM 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>
> > ---
> >  drivers/base/core.c | 55 ++++++++++++++++++++-------------------------
> >  1 file changed, 24 insertions(+), 31 deletions(-)
> >
> > Tomi,
> >
> > Thanks for all the testing and debugging help! And do use
> > post-init-providers even with this patch to improve ordering
> > enforcement. I probably should change the cycle log from info to warn in
> > a separate patch :)
> >
> > Greg,
> >
> > I no longer have concerns about pulling this into 6.13. But we can give
> > a week or so to Geert/Francesco to do some additional testing.
> >
> > Geert/Francesco,
> 
> Heads up. Greg has pulled this into driver-core git's
> driver-core-testing branch. Which means in a week or two it'll get
> into the actual driver-core-next branch. So, if you want to do
> additional testing, you might want to jump on it soon.

It should now show up in the next linux-next release.

thanks,

greg k-h