From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7559C2FA624; Tue, 17 Jun 2025 16:59:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750179592; cv=none; b=hblZbkPZPY2ptjPvhsv4LjVbIOu4cu0tmBFG8dtkTKpalSrcL7F+PHSeGLD86MSB89MsTMvrq3kWZ3vNWxuKjPWS3MJm4khwLBfrnFGxKPuuTwEK8Z6iMP8ccS1/eNrXP1ITT4w+2k4zQhQZYvhPIWf7m1GP/EIhPHxUcvMvIzU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750179592; c=relaxed/simple; bh=cpdFqG8VE3oUn40geLA2DBr+wtB8mZ02xKcGoI5IPQY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Xqbcjmhn6xdbITEY55U0v2jzFIHKHF9s/YyI3GoaVuKNYWHPGLAlu/f9hQ7EJ7f8+Xwf3RiW9t2aUvNGc1qZj403Boumfsoyi0spTqYmxT1b6/6+kkB9rBmmslr6zXbzcX+8afa2QpB07QcOkZhQTpM6H9UgEEkX0swOVOzbt7o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=U05IuaD1; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="U05IuaD1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D7AB8C4CEE3; Tue, 17 Jun 2025 16:59:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1750179592; bh=cpdFqG8VE3oUn40geLA2DBr+wtB8mZ02xKcGoI5IPQY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=U05IuaD1bJIohe7AWSw6RJtjOsWhQJenPkMDttC2JsPV3u/WK0613Q2jx++HkMUqe OY+GtUyehrqkNdtyVyTeOfN9yIeaQMOHKzrIA0dMNtJEYb5uzaIRYyK9qF2ua345cz 91yICdBzyCvdLXb/bho0HFh42Zr572zghzcqmOeQ= Date: Tue, 17 Jun 2025 17:49:49 +0200 From: Greg Kroah-Hartman To: Sean Anderson Cc: Saravana Kannan , "Rafael J . Wysocki" , Danilo Krummrich , linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, Christoph Hellwig , Rob Herring , Grant Likely Subject: Re: [PATCH] driver core: Prevent deferred probe loops Message-ID: <2025061740-banter-acclaim-2006@gregkh> References: <20250610183459.3395328-1-sean.anderson@linux.dev> <2025061147-squishier-oversleep-80cd@gregkh> <7d6d8789-e10b-4b06-aa99-5c1a1bdd3b4c@linux.dev> <70958a2e-abc8-4894-b99a-f2981db9981f@linux.dev> <2025061700-unmapped-labrador-a8c9@gregkh> <0ee2f641-c3f3-4a3a-87b4-e1279a862d68@linux.dev> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <0ee2f641-c3f3-4a3a-87b4-e1279a862d68@linux.dev> On Tue, Jun 17, 2025 at 11:35:04AM -0400, Sean Anderson wrote: > On 6/17/25 04:50, Greg Kroah-Hartman wrote: > > On Thu, Jun 12, 2025 at 04:40:48PM -0400, Sean Anderson wrote: > >> On 6/12/25 13:56, Saravana Kannan wrote: > >> > On Thu, Jun 12, 2025 at 8:53 AM Sean Anderson wrote: > >> >> > >> >> On 6/11/25 08:23, Greg Kroah-Hartman wrote: > >> >> > On Tue, Jun 10, 2025 at 07:44:27PM -0400, Sean Anderson wrote: > >> >> >> On 6/10/25 19:32, Saravana Kannan wrote: > >> >> >> > On Tue, Jun 10, 2025 at 11:35 AM Sean Anderson wrote: > >> >> >> >> > >> >> >> >> A deferred probe loop can occur when a device returns EPROBE_DEFER after > >> >> >> >> registering a bus with children: > >> >> >> > > >> >> >> > This is a broken driver. A parent device shouldn't register child > >> >> >> > devices unless it is fully read itself. It's not logical to say the > >> >> >> > child devices are available, if the parent itself isn't fully ready. > >> >> >> > So, adding child devices/the bus should be the last thing done in the > >> >> >> > parent's probe function. > >> >> >> > > >> >> >> > I know there are odd exceptions where the parent depends on the child, > >> >> >> > so they might add the child a bit earlier in the probe > >> >> >> > >> >> >> This is exactly the case here. So the bus probing cannot happen any > >> >> >> later than it already does. > >> >> > > >> >> > Please fix the driver not to do this. > >> >> > >> >> How? The driver needs the PCS to work. And the PCS can live on the MDIO > >> >> bus. > >> > > >> > Obviously I don't know the full details, but you could implement it as > >> > MFD. So the bus part would not get removed even if the PCS fails to > >> > probe. Then the PCS can probe when whatever it needs ends up probing. > >> > >> I was thinking about making the MDIO bus a separate device. But I think > >> it will be tricky to get suspend/resume working correctly. And this > >> makes conversions more difficult because you cannot just add some > >> pcs_get/pcs_put calls, you have to split out the MDIO bus too (which is > >> invariably created as a child of the MAC). > >> > >> And what happens if a developer doesn't realize they have to split off > >> the MDIO bus before converting? Everything works fine, except if there > >> is some problem loading the PCS driver, which they may not test. Is this > >> prohibition against failing after creating a bus documented anywhere? I > >> don't recall seeing it... > > > > What do you mean "failing after creating a bus"? If a bus is failed to > > be created, you fail like normal, no difference here. > > Creating the bus is successful, but there's an EPROBE_DEFER failure after > that. Which induces the probe loop as described in my initial email. Then don't allow a defer to happen :) Or better yet, just succeed and spin up a new thread for the new bus to attach it's devices to. That's what many other busses do today. thanks, greg k-h