linux-kernel - Re: [PATCH 04/23] interconnect: imx: fix registration race

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Date:   Mon, 6 Feb 2023 21:52:33 +0100
From:   Luca Ceresoli <luca.ceresoli@...tlin.com>
To:     Johan Hovold <johan@...nel.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Georgi Djakov <djakov@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Artur Świgoń <a.swigon@...sung.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Leonard Crestez <leonard.crestez@....com>,
        Alexandre Bailon <abailon@...libre.com>
Subject: Re: [PATCH 04/23] interconnect: imx: fix registration race

Hello Johan,

On Mon, 6 Feb 2023 09:09:50 +0100
Johan Hovold <johan@...nel.org> wrote:

> On Fri, Feb 03, 2023 at 05:01:21PM +0100, Luca Ceresoli wrote:
> > Hello Johan,
> > 
> > On Wed,  1 Feb 2023 11:15:40 +0100
> > Johan Hovold <johan+linaro@...nel.org> wrote:
> >   
> > > The current interconnect provider registration interface is inherently
> > > racy as nodes are not added until the after adding the provider. This
> > > can specifically cause racing DT lookups to fail.
> > > 
> > > Switch to using the new API where the provider is not registered until
> > > after it has been fully initialised.
> > > 
> > > Fixes: f0d8048525d7 ("interconnect: Add imx core driver")
> > > Cc: stable@...r.kernel.org      # 5.8
> > > Cc: Leonard Crestez <leonard.crestez@....com>
> > > Cc: Alexandre Bailon <abailon@...libre.com>
> > > Signed-off-by: Johan Hovold <johan+linaro@...nel.org>  
> > 
> > Georgi pointed me to this series after I reported a bug yesterday [0],
> > that I found on iMX8MP. So I ran some tests with my original, failing
> > tree, minus one patch with my debugging code to hunt for the bug, plus
> > patches 1-4 of this series.
> > 
> > The original code was failing approx 5~10% of the times. With your 4
> > patches applied it ran 139 times with zero errors, which looks great! I
> > won't be able to do more testing until next Monday to be extra sure.  
> 
> Thanks for testing.
> 
> It indeed looks like you're hitting the same race, and as the imx
> interconnect driver also initialises the provider data num_nodes count
> before adding the nodes it results in that NULL-deref (where the qcom
> driver failed a bit more gracefully).

My v6.2-rc5 tree with patches 1 to 4 added has booted 590 times with 0
errors, which add to the 139 times on Friday. This definitely deserves
my:

Tested-by: Luca Ceresoli <luca.ceresoli@...tlin.com>

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com