From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [78.32.30.218]) (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 DAAAA81207 for ; Tue, 23 Jan 2024 20:08:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=78.32.30.218 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706040484; cv=none; b=Db3sYeDGEyvJXBfDkhbjJJKLr09lLQNbGmmTMGGOYg6ji0jIkxu2kEy1NL4a08QrTifqx1t/HEGhjJdrxxLql9jbbYVOt2WzzYvmuhA6HlDVhY3icFWEgFP4OeP772rwrtM7WmvcmiUJFGcQOvyF0TFY4vR1WDxYc28IZ04Ds1w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706040484; c=relaxed/simple; bh=9I/UsS8y9mGIMpG+pdPW0Jhzyh9UOzbZXYsmZioHbIE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=gA9UdbNWaI40rnZQYwX4w1ikYasNYYK76Hf9VjmqC/oCmbx0CCqbdHmjz8dvxuLkWB58wGBwXGrJdEAmmHdAEK2fZYw4qofHxcrC/Ge1mLmQdts7zrcGipaFUmuATA/bILcg80Nl7eKxNtRwEC5v3YUdvsh9y5ZOBpAuq8uYWWQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=armlinux.org.uk; spf=none smtp.mailfrom=armlinux.org.uk; dkim=pass (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b=m+UMwDvC; arc=none smtp.client-ip=78.32.30.218 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=armlinux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=armlinux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b="m+UMwDvC" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=/K+NKUpNvuWFdvNqRH7z18FAACuRlVImuRGe1xvHS08=; b=m+UMwDvCAx9RXnWkGffmkb13Mq gvAcm/JJcDX+/sH+P1uXjviNELKu+Kpzh9pR9WCP0YhjMPPrLyIygSRxkOU6de2lAq5UHxkkZNsws o386r0pOIN50Z5R0L/jEvLcglJo1D54FmiZzs9iQ8W2NWKTaDMviT4/WwaxrhMvj8z8b7hBs23gSk Ke5hBSU+IoA7EHTwyr2cc7pWNebZhowOSAK8PSrhh8+egmH1R/e+2YPbDqPSlQox6Fzr812onfsoi xtNmvydKPoJI0F7ci262ZxmruhRmnG7HzUB3dPDIjtQ8iHPj0bN7Xk7y5758m6aPH01q99KLFIZP4 SKSGPhJQ==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:46540) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1rSN3f-00031R-1S; Tue, 23 Jan 2024 20:07:43 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1rSN3X-0002Ct-RA; Tue, 23 Jan 2024 20:07:35 +0000 Date: Tue, 23 Jan 2024 20:07:35 +0000 From: "Russell King (Oracle)" To: Sean Anderson Cc: Landen.Chao@mediatek.com, UNGLinuxDriver@microchip.com, alexandre.belloni@bootlin.com, andrew@lunn.ch, angelogioacchino.delregno@collabora.com, arinc.unal@arinc9.com, claudiu.manoil@nxp.com, daniel@makrotopia.org, davem@davemloft.net, dqfext@gmail.com, edumazet@google.com, f.fainelli@gmail.com, hkallweit1@gmail.com, kuba@kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, matthias.bgg@gmail.com, netdev@vger.kernel.org, olteanv@gmail.com, pabeni@redhat.com, sean.wang@mediatek.com Subject: Re: [PATCH RFC net-next 03/14] net: phylink: add support for PCS link change notifications Message-ID: References: <75773076-39a2-49dd-9eb2-15a10955a60d@seco.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <75773076-39a2-49dd-9eb2-15a10955a60d@seco.com> Sender: Russell King (Oracle) On Tue, Jan 23, 2024 at 02:46:15PM -0500, Sean Anderson wrote: > Hi Russell, > > Does there need to be any locking when calling phylink_pcs_change? I > noticed that you call it from threaded IRQ context in [1]. Can that race > with phylink_major_config? What kind of scenario are you thinking may require locking? I guess the possibility would be if pcs->phylink changes and the compiler reads it multiple times - READ_ONCE() should solve that. However, in terms of the mechanics, there's no race. During the initial bringup, the resolve worker isn't started until after phylink_major_config() has completed (it's started at phylink_enable_and_run_resolve().) So, if phylink_pcs_change() gets called while in phylink_major_config() there, it'll see that pl->phylink_disable_state is non-zero, and won't queue the work. The next one is within the worker itself - and there can only be one instance of the worker running in totality. So, if phylink_pcs_change() gets called while phylink_major_config() is running from this path, the only thing it'll do is re-schedule the resolve worker to run another iteration which is harmless (whether or not the PCS is still current.) The last case is phylink_ethtool_ksettings_set(). This runs under the state_mutex, which locks out the resolve worker (since it also takes that mutex). So calling phylink_pcs_change() should be pretty harmless _unless_ the compiler re-reads pcs->phylink multiple times inside phylink_pcs_change(), which I suppose with modern compilers is possible. Hence my suggestion above about READ_ONCE() for that. Have you encountered an OOPS because pcs->phylink has become NULL? Or have you spotted another issue? -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!