linux-kernel - Re: [PATCH] opp: use list iterator only inside the loop

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Date:   Thu, 31 Mar 2022 10:20:09 +0800
From:   Xiaomeng Tong <xiam0nd.tong@...il.com>
To:     viresh.kumar@...aro.org
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, nm@...com,
        sboyd@...nel.org, vireshk@...nel.org, xiam0nd.tong@...il.com
Subject: Re: [PATCH] opp: use list iterator only inside the loop

On  Thu, 31 Mar 2022 07:42:35 +0530, Viresh Kumar wrote:

> Hi Xiaomeng,
> 
> On 31-03-22, 09:58, Xiaomeng Tong wrote:
> >     dev = new_dev->dev;
> 
> Why is this added here ?

Sorry for that. I will delete it in next patch.

> 
> > 
> > As discussed before,
> 
> Please remember that whatever you write here will go in the commit
> logs for ever and no one will ever know what you discussed and with
> whom.
> 
> This area should describe the problem at hand.
> 

ok, thank you for the suggestion.

> > we should avoid to use a list iterator variable
> > outside the loop which is considered harmful[1].
> > 
> > In this case, use a new variable 'iter' as the list iterator, while
> > use the old variable 'new_dev' as a dedicated pointer to point to the
> > found entry.
> > 
> > [1]:  https://lkml.org/lkml/2022/2/17/1032
> > 
> > Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
> > ---
> >  drivers/opp/debugfs.c | 11 ++++++++---
> >  1 file changed, 8 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/opp/debugfs.c b/drivers/opp/debugfs.c
> > index 596c185b5dda..a4476985e4ce 100644
> > --- a/drivers/opp/debugfs.c
> > +++ b/drivers/opp/debugfs.c
> > @@ -187,14 +187,19 @@ void opp_debug_register(struct opp_device *opp_dev, struct opp_table *opp_table)
> >  static void opp_migrate_dentry(struct opp_device *opp_dev,
> >  			       struct opp_table *opp_table)
> >  {
> > -	struct opp_device *new_dev;
> > +	struct opp_device *new_dev = NULL, *iter;
> >  	const struct device *dev;
> >  	struct dentry *dentry;
> >  
> >  	/* Look for next opp-dev */
> > -	list_for_each_entry(new_dev, &opp_table->dev_list, node)
> > -		if (new_dev != opp_dev)
> > +	list_for_each_entry(iter, &opp_table->dev_list, node)
> > +		if (iter != opp_dev) {
> > +			new_dev = iter;
> >  			break;
> > +		}
> > +
> > +	if (!new_dev)
> 
> I will rather make this BUG_ON(!new_dev);
> 

Ok, i will take it.

> > +		return;
> >  
> >  	/* new_dev is guaranteed to be valid here */
> >  	dev = new_dev->dev;

--
Xiaomeng Tong