linux-kernel - Re: [PATCH 2/2] clk: pmc-atom: use devm_kstrdup

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Date:   Mon, 27 Aug 2018 15:52:27 +0300
From:   Mike Rapoport <rppt@...ux.vnet.ibm.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Arend van Spriel <aspriel@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Robin Murphy <robin.murphy@....com>,
        Joe Perches <joe@...ches.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jonathan Corbet <corbet@....net>, Roman Gushchin <guro@...com>,
        Huang Ying <ying.huang@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org
Subject: Re: [PATCH 2/2] clk: pmc-atom: use devm_kstrdup_const()

On Mon, Aug 27, 2018 at 02:28:45PM +0200, Bartosz Golaszewski wrote:
> 2018-08-27 12:39 GMT+02:00 Mike Rapoport <rppt@...ux.vnet.ibm.com>:
> > On Mon, Aug 27, 2018 at 10:21:01AM +0200, Bartosz Golaszewski wrote:
> >> Use devm_kstrdup_const() in the pmc-atom driver. This mostly serves as
> >> an example of how to use this new routine to shrink driver code.
> >>
> >> While we're at it: replace a call to kcalloc() with devm_kcalloc().
> >>
> >> Signed-off-by: Bartosz Golaszewski <brgl@...ev.pl>
> >> ---
> >>  drivers/clk/x86/clk-pmc-atom.c | 19 ++++---------------
> >>  1 file changed, 4 insertions(+), 15 deletions(-)
> >>
> >> diff --git a/drivers/clk/x86/clk-pmc-atom.c b/drivers/clk/x86/clk-pmc-atom.c
> >> index 08ef69945ffb..daa2192e6568 100644
> >> --- a/drivers/clk/x86/clk-pmc-atom.c
> >> +++ b/drivers/clk/x86/clk-pmc-atom.c
> >> @@ -253,14 +253,6 @@ static void plt_clk_unregister_fixed_rate_loop(struct clk_plt_data *data,
> >>               plt_clk_unregister_fixed_rate(data->parents[i]);
> >>  }
> >>
> >> -static void plt_clk_free_parent_names_loop(const char **parent_names,
> >> -                                        unsigned int i)
> >> -{
> >> -     while (i--)
> >> -             kfree_const(parent_names[i]);
> >> -     kfree(parent_names);
> >> -}
> >> -
> >>  static void plt_clk_unregister_loop(struct clk_plt_data *data,
> >>                                   unsigned int i)
> >>  {
> >> @@ -286,8 +278,8 @@ static const char **plt_clk_register_parents(struct platform_device *pdev,
> >>       if (!data->parents)
> >>               return ERR_PTR(-ENOMEM);
> >>
> >> -     parent_names = kcalloc(nparents, sizeof(*parent_names),
> >> -                            GFP_KERNEL);
> >> +     parent_names = devm_kcalloc(&pdev->dev, nparents,
> >> +                                 sizeof(*parent_names), GFP_KERNEL);
> >>       if (!parent_names)
> >>               return ERR_PTR(-ENOMEM);
> >>
> >> @@ -300,7 +292,8 @@ static const char **plt_clk_register_parents(struct platform_device *pdev,
> >>                       err = PTR_ERR(data->parents[i]);
> >>                       goto err_unreg;
> >>               }
> >> -             parent_names[i] = kstrdup_const(clks[i].name, GFP_KERNEL);
> >> +             parent_names[i] = devm_kstrdup_const(&pdev->dev,
> >> +                                                  clks[i].name, GFP_KERNEL);
> >>       }
> >>
> >>       data->nparents = nparents;
> >> @@ -308,7 +301,6 @@ static const char **plt_clk_register_parents(struct platform_device *pdev,
> >>
> >>  err_unreg:
> >>       plt_clk_unregister_fixed_rate_loop(data, i);
> >> -     plt_clk_free_parent_names_loop(parent_names, i);
> >
> > What happens if clks[i].name is not a part of RO data? The devm_kstrdup_const
> > will allocate memory and nothing will ever free it...
> >
> 
> I'm looking at it and trying to see if I'm missing something, but
> AFAIK the whole concept of devm_* is to leave out the resource
> management part.
> 
> devm_kstrdup_const() will internally call devm_kstrdup() for strings
> that are not in .rodata and once the device is detached, the string
> will be freed (or not if it's in .rodata).

And when it's going to be freed, how the resource management will know
whether it's .rodata or not?
 
> BR
> Bart
> 
> > And, please don't drop kfree(parent_names) here.
> >
> >>       return ERR_PTR(err);
> >>  }
> >>
> >> @@ -351,15 +343,12 @@ static int plt_clk_probe(struct platform_device *pdev)
> >>               goto err_unreg_clk_plt;
> >>       }
> >>
> >> -     plt_clk_free_parent_names_loop(parent_names, data->nparents);
> >> -
> >>       platform_set_drvdata(pdev, data);
> >>       return 0;
> >>
> >>  err_unreg_clk_plt:
> >>       plt_clk_unregister_loop(data, i);
> >>       plt_clk_unregister_parents(data);
> >> -     plt_clk_free_parent_names_loop(parent_names, data->nparents);
> >
> > Ditto.
> >
> >>       return err;
> >>  }
> >>
> >> --
> >> 2.18.0
> >>
> >
> > --
> > Sincerely yours,
> > Mike.
> >
> 

-- 
Sincerely yours,
Mike.