linux-kernel - Re: [PATCH] coresight: etm4x: Ensure valid drvdata and clock before clk

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Message-ID: <201aae70-c555-45ce-9944-f8645feb54f6@kadam.mountain>
Date:   Fri, 11 Aug 2023 12:26:58 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     James Clark <james.clark@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Mike Leach <mike.leach@...aro.org>, coresight@...ts.linaro.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] coresight: etm4x: Ensure valid drvdata and clock before
 clk_put()

On Fri, Aug 11, 2023 at 10:09:43AM +0100, Suzuki K Poulose wrote:
> On 11/08/2023 09:39, James Clark wrote:
> > 
> > 
> > On 11/08/2023 07:27, Anshuman Khandual wrote:
> > > This validates 'drvdata' and 'drvdata->pclk' clock before calling clk_put()
> > > in etm4_remove_platform_dev(). The problem was detected using Smatch static
> > > checker as reported.
> > > 
> > > Cc: Suzuki K Poulose <suzuki.poulose@....com>
> > > Cc: Mike Leach <mike.leach@...aro.org>
> > > Cc: James Clark <james.clark@....com>
> > > Cc: coresight@...ts.linaro.org
> > > Cc: linux-arm-kernel@...ts.infradead.org
> > > Cc: linux-kernel@...r.kernel.org
> > > Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
> > > Closes: https://lists.linaro.org/archives/list/coresight@lists.linaro.org/thread/G4N6P4OXELPLLQSNU3GU2MR4LOLRXRMJ/
> > > Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> > > ---
> > > This applies on coresight-next
> > > 
> > >   drivers/hwtracing/coresight/coresight-etm4x-core.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > > index 703b6fcbb6a5..eb412ce302cc 100644
> > > --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > > +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > > @@ -2269,7 +2269,7 @@ static int __exit etm4_remove_platform_dev(struct platform_device *pdev)
> > >   		etm4_remove_dev(drvdata);
> > >   	pm_runtime_disable(&pdev->dev);
> > > -	if (drvdata->pclk)
> > > +	if (drvdata && drvdata->pclk && !IS_ERR(drvdata->pclk))
> > >   		clk_put(drvdata->pclk);
> > >   	return 0;
> > 
> > It could be !IS_ERR_OR_NULL(drvdata->pclk), but I wouldn't bother
> > changing it at this point.
> 
> +1, please could we have that. Someone else will run a code scanner and
> send a patch later. Given this is straight and easy change, lets do it
> in the first place.

drvdata->pclk can't actually be an error pointer.  probe() will
correctly not allow that.  All the IS_ERR(drvdata->pclk) checks should
be removed except for the first check in probe().

There is also no need to check "drvdata->pclk" for NULL because
clk_put() accepts NULL pointers.  (Returning NULL means the clk
subsystem has been disabled deliberately).

Also drvdata can't actually be NULL either.

regards,
dan carpenter