[PATCH 1/2] devres: provide devm_kstrdup_const()

[PATCH 1/2] devres: provide devm_kstrdup_const()

[Bartosz Golaszewski]

Provide a resource managed version of kstrdup_const(). This variant
internally calls devm_kstrdup() on pointers that are outside of
.rodata section. Also provide a corresponding version of devm_kfree().

Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
---
 include/linux/device.h |  2 ++
 mm/util.c              | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/include/linux/device.h b/include/linux/device.h
index 8f882549edee..f8f5982d26b2 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -693,7 +693,9 @@ static inline void *devm_kcalloc(struct device *dev,
 	return devm_kmalloc_array(dev, n, size, flags | __GFP_ZERO);
 }
 extern void devm_kfree(struct device *dev, void *p);
+extern void devm_kfree_const(struct device *dev, void *p);
 extern char *devm_kstrdup(struct device *dev, const char *s, gfp_t gfp) __malloc;
+extern char *devm_kstrdup_const(struct device *dev, const char *s, gfp_t gfp);
 extern void *devm_kmemdup(struct device *dev, const void *src, size_t len,
 			  gfp_t gfp);
 
diff --git a/mm/util.c b/mm/util.c
index d2890a407332..6d1f41b5775e 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -39,6 +39,20 @@ void kfree_const(const void *x)
 }
 EXPORT_SYMBOL(kfree_const);
 
+/**
+ * devm_kfree_const - Resource managed conditional kfree
+ * @dev: device this memory belongs to
+ * @p: memory to free
+ *
+ * Function calls devm_kfree only if @p is not in .rodata section.
+ */
+void devm_kfree_const(struct device *dev, void *p)
+{
+	if (!is_kernel_rodata((unsigned long)p))
+		devm_kfree(dev, p);
+}
+EXPORT_SYMBOL(devm_kfree_const);
+
 /**
  * kstrdup - allocate space for and copy an existing string
  * @s: the string to duplicate
@@ -78,6 +92,27 @@ const char *kstrdup_const(const char *s, gfp_t gfp)
 }
 EXPORT_SYMBOL(kstrdup_const);
 
+/**
+ * devm_kstrdup_const - resource managed conditional string duplication
+ * @dev: device for which to duplicate the string
+ * @s: the string to duplicate
+ * @gfp: the GFP mask used in the kmalloc() call when allocating memory
+ *
+ * Function returns source string if it is in .rodata section otherwise it
+ * fallbacks to devm_kstrdup.
+ *
+ * Strings allocated by devm_kstrdup_const will be automatically freed when
+ * the associated device is detached.
+ */
+char *devm_kstrdup_const(struct device *dev, const char *s, gfp_t gfp)
+{
+	if (is_kernel_rodata((unsigned long)s))
+		return s;
+
+	return devm_kstrdup(dev, s, gfp);
+}
+EXPORT_SYMBOL(devm_kstrdup_const);
+
 /**
  * kstrndup - allocate space for and copy an existing string
  * @s: the string to duplicate
-- 
2.18.0

[PATCH 2/2] clk: pmc-atom: use devm_kstrdup_const()

[Bartosz Golaszewski]

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@bgdev.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);
 	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);
 	return err;
 }
 
-- 
2.18.0

Re: [PATCH 2/2] clk: pmc-atom: use devm_kstrdup_const()

[Mike Rapoport]

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@bgdev.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...

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.

Re: [PATCH 2/2] clk: pmc-atom: use devm_kstrdup_const()

[Bartosz Golaszewski]

2018-08-27 12:39 GMT+02:00 Mike Rapoport <rppt@linux.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@bgdev.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).

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.
>

Re: [PATCH 2/2] clk: pmc-atom: use devm_kstrdup_const()

[Mike Rapoport]

On Mon, Aug 27, 2018 at 02:28:45PM +0200, Bartosz Golaszewski wrote:
> 2018-08-27 12:39 GMT+02:00 Mike Rapoport <rppt@linux.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@bgdev.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.

Re: [PATCH 2/2] clk: pmc-atom: use devm_kstrdup_const()

[Bartosz Golaszewski]

2018-08-27 14:52 GMT+02:00 Mike Rapoport <rppt@linux.vnet.ibm.com>:
> On Mon, Aug 27, 2018 at 02:28:45PM +0200, Bartosz Golaszewski wrote:
>> 2018-08-27 12:39 GMT+02:00 Mike Rapoport <rppt@linux.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@bgdev.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?
>

If the string to be duplicated is in .rodata, it's returned as is from
devm_kstrdup_const(). Never gets added to the devres list, never get's
freed. When the string to be duplicated is not in .rodata,
devm_kstrdup() is called from devm_kstrdup_const(). Now the string is
in the devres list of this device and it will get freed on driver
detach. I really don't see what else could be a problem here.

BR
Bart

>> 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.
>

Re: [PATCH 2/2] clk: pmc-atom: use devm_kstrdup_const()

[Mike Rapoport]

On Mon, Aug 27, 2018 at 02:58:46PM +0200, Bartosz Golaszewski wrote:
> 2018-08-27 14:52 GMT+02:00 Mike Rapoport <rppt@linux.vnet.ibm.com>:
> > On Mon, Aug 27, 2018 at 02:28:45PM +0200, Bartosz Golaszewski wrote:
> >> 2018-08-27 12:39 GMT+02:00 Mike Rapoport <rppt@linux.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@bgdev.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?
> >
> 
> If the string to be duplicated is in .rodata, it's returned as is from
> devm_kstrdup_const(). Never gets added to the devres list, never get's
> freed. When the string to be duplicated is not in .rodata,
> devm_kstrdup() is called from devm_kstrdup_const(). Now the string is
> in the devres list of this device and it will get freed on driver
> detach. I really don't see what else could be a problem here.

Thanks for the clarification.
I think that it's worth adding a similar explanation to the changelog of
the first patch.
 
> BR
> Bart
> 
> >> 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.
> >
> 

-- 
Sincerely yours,
Mike.

Re: [PATCH 1/2] devres: provide devm_kstrdup_const()

[Joe Perches]

On Mon, 2018-08-27 at 10:21 +0200, Bartosz Golaszewski wrote:
> Provide a resource managed version of kstrdup_const(). This variant
> internally calls devm_kstrdup() on pointers that are outside of
> .rodata section. Also provide a corresponding version of devm_kfree().
[]
> diff --git a/mm/util.c b/mm/util.c
[]
>  /**
>   * kstrdup - allocate space for and copy an existing string
>   * @s: the string to duplicate
> @@ -78,6 +92,27 @@ const char *kstrdup_const(const char *s, gfp_t gfp)
>  }
>  EXPORT_SYMBOL(kstrdup_const);
>  
> +/**
> + * devm_kstrdup_const - resource managed conditional string duplication
> + * @dev: device for which to duplicate the string
> + * @s: the string to duplicate
> + * @gfp: the GFP mask used in the kmalloc() call when allocating memory
> + *
> + * Function returns source string if it is in .rodata section otherwise it
> + * fallbacks to devm_kstrdup.
> + *
> + * Strings allocated by devm_kstrdup_const will be automatically freed when
> + * the associated device is detached.
> + */
> +char *devm_kstrdup_const(struct device *dev, const char *s, gfp_t gfp)
> +{
> +	if (is_kernel_rodata((unsigned long)s))
> +		return s;
> +
> +	return devm_kstrdup(dev, s, gfp);
> +}
> +EXPORT_SYMBOL(devm_kstrdup_const);

Doesn't this lose constness and don't you get
a compiler warning here?

The kstrdup_const function returns a const char *,
why shouldn't this?

Re: [PATCH 1/2] devres: provide devm_kstrdup_const()

[Bartosz Golaszewski]

2018-08-27 10:42 GMT+02:00 Joe Perches <joe@perches.com>:
> On Mon, 2018-08-27 at 10:21 +0200, Bartosz Golaszewski wrote:
>> Provide a resource managed version of kstrdup_const(). This variant
>> internally calls devm_kstrdup() on pointers that are outside of
>> .rodata section. Also provide a corresponding version of devm_kfree().
> []
>> diff --git a/mm/util.c b/mm/util.c
> []
>>  /**
>>   * kstrdup - allocate space for and copy an existing string
>>   * @s: the string to duplicate
>> @@ -78,6 +92,27 @@ const char *kstrdup_const(const char *s, gfp_t gfp)
>>  }
>>  EXPORT_SYMBOL(kstrdup_const);
>>
>> +/**
>> + * devm_kstrdup_const - resource managed conditional string duplication
>> + * @dev: device for which to duplicate the string
>> + * @s: the string to duplicate
>> + * @gfp: the GFP mask used in the kmalloc() call when allocating memory
>> + *
>> + * Function returns source string if it is in .rodata section otherwise it
>> + * fallbacks to devm_kstrdup.
>> + *
>> + * Strings allocated by devm_kstrdup_const will be automatically freed when
>> + * the associated device is detached.
>> + */
>> +char *devm_kstrdup_const(struct device *dev, const char *s, gfp_t gfp)
>> +{
>> +     if (is_kernel_rodata((unsigned long)s))
>> +             return s;
>> +
>> +     return devm_kstrdup(dev, s, gfp);
>> +}
>> +EXPORT_SYMBOL(devm_kstrdup_const);
>
> Doesn't this lose constness and don't you get
> a compiler warning here?
>

Yes it does but for some reason gcc 6.3 didn't complain...

> The kstrdup_const function returns a const char *,
> why shouldn't this?
>

It probably should, I'll fix it for v2.

Bart

Re: [PATCH 1/2] devres: provide devm_kstrdup_const()

[Mike Rapoport]

On Mon, Aug 27, 2018 at 10:21:00AM +0200, Bartosz Golaszewski wrote:
> Provide a resource managed version of kstrdup_const(). This variant
> internally calls devm_kstrdup() on pointers that are outside of
> .rodata section. Also provide a corresponding version of devm_kfree().
> 
> Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
> ---
>  include/linux/device.h |  2 ++
>  mm/util.c              | 35 +++++++++++++++++++++++++++++++++++
>  2 files changed, 37 insertions(+)
> 
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 8f882549edee..f8f5982d26b2 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -693,7 +693,9 @@ static inline void *devm_kcalloc(struct device *dev,
>  	return devm_kmalloc_array(dev, n, size, flags | __GFP_ZERO);
>  }
>  extern void devm_kfree(struct device *dev, void *p);
> +extern void devm_kfree_const(struct device *dev, void *p);
>  extern char *devm_kstrdup(struct device *dev, const char *s, gfp_t gfp) __malloc;
> +extern char *devm_kstrdup_const(struct device *dev, const char *s, gfp_t gfp);
>  extern void *devm_kmemdup(struct device *dev, const void *src, size_t len,
>  			  gfp_t gfp);
> 
> diff --git a/mm/util.c b/mm/util.c
> index d2890a407332..6d1f41b5775e 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -39,6 +39,20 @@ void kfree_const(const void *x)
>  }
>  EXPORT_SYMBOL(kfree_const);
> 
> +/**
> + * devm_kfree_const - Resource managed conditional kfree
> + * @dev: device this memory belongs to
> + * @p: memory to free
> + *
> + * Function calls devm_kfree only if @p is not in .rodata section.
> + */
> +void devm_kfree_const(struct device *dev, void *p)
> +{
> +	if (!is_kernel_rodata((unsigned long)p))
> +		devm_kfree(dev, p);
> +}
> +EXPORT_SYMBOL(devm_kfree_const);
> +
>  /**
>   * kstrdup - allocate space for and copy an existing string
>   * @s: the string to duplicate
> @@ -78,6 +92,27 @@ const char *kstrdup_const(const char *s, gfp_t gfp)
>  }
>  EXPORT_SYMBOL(kstrdup_const);
> 
> +/**
> + * devm_kstrdup_const - resource managed conditional string duplication
> + * @dev: device for which to duplicate the string
> + * @s: the string to duplicate
> + * @gfp: the GFP mask used in the kmalloc() call when allocating memory
> + *
> + * Function returns source string if it is in .rodata section otherwise it
> + * fallbacks to devm_kstrdup.

Please make it proper "Returns:" description and move to the end of the
comment. See Documentation/doc-guide/kernel-doc.rst.

> + * Strings allocated by devm_kstrdup_const will be automatically freed when
> + * the associated device is detached.
> + */
> +char *devm_kstrdup_const(struct device *dev, const char *s, gfp_t gfp)
> +{
> +	if (is_kernel_rodata((unsigned long)s))
> +		return s;
> +
> +	return devm_kstrdup(dev, s, gfp);
> +}
> +EXPORT_SYMBOL(devm_kstrdup_const);
> +

The devm_ variants seem to belong to drivers/base/devres.c rather than
mm/util.c

>  /**
>   * kstrndup - allocate space for and copy an existing string
>   * @s: the string to duplicate
> -- 
> 2.18.0
> 

-- 
Sincerely yours,
Mike.

Re: [PATCH 1/2] devres: provide devm_kstrdup_const()

[Bartosz Golaszewski]

2018-08-27 12:33 GMT+02:00 Mike Rapoport <rppt@linux.vnet.ibm.com>:
> On Mon, Aug 27, 2018 at 10:21:00AM +0200, Bartosz Golaszewski wrote:
>> Provide a resource managed version of kstrdup_const(). This variant
>> internally calls devm_kstrdup() on pointers that are outside of
>> .rodata section. Also provide a corresponding version of devm_kfree().
>>
>> Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
>> ---
>>  include/linux/device.h |  2 ++
>>  mm/util.c              | 35 +++++++++++++++++++++++++++++++++++
>>  2 files changed, 37 insertions(+)
>>
>> diff --git a/include/linux/device.h b/include/linux/device.h
>> index 8f882549edee..f8f5982d26b2 100644
>> --- a/include/linux/device.h
>> +++ b/include/linux/device.h
>> @@ -693,7 +693,9 @@ static inline void *devm_kcalloc(struct device *dev,
>>       return devm_kmalloc_array(dev, n, size, flags | __GFP_ZERO);
>>  }
>>  extern void devm_kfree(struct device *dev, void *p);
>> +extern void devm_kfree_const(struct device *dev, void *p);
>>  extern char *devm_kstrdup(struct device *dev, const char *s, gfp_t gfp) __malloc;
>> +extern char *devm_kstrdup_const(struct device *dev, const char *s, gfp_t gfp);
>>  extern void *devm_kmemdup(struct device *dev, const void *src, size_t len,
>>                         gfp_t gfp);
>>
>> diff --git a/mm/util.c b/mm/util.c
>> index d2890a407332..6d1f41b5775e 100644
>> --- a/mm/util.c
>> +++ b/mm/util.c
>> @@ -39,6 +39,20 @@ void kfree_const(const void *x)
>>  }
>>  EXPORT_SYMBOL(kfree_const);
>>
>> +/**
>> + * devm_kfree_const - Resource managed conditional kfree
>> + * @dev: device this memory belongs to
>> + * @p: memory to free
>> + *
>> + * Function calls devm_kfree only if @p is not in .rodata section.
>> + */
>> +void devm_kfree_const(struct device *dev, void *p)
>> +{
>> +     if (!is_kernel_rodata((unsigned long)p))
>> +             devm_kfree(dev, p);
>> +}
>> +EXPORT_SYMBOL(devm_kfree_const);
>> +
>>  /**
>>   * kstrdup - allocate space for and copy an existing string
>>   * @s: the string to duplicate
>> @@ -78,6 +92,27 @@ const char *kstrdup_const(const char *s, gfp_t gfp)
>>  }
>>  EXPORT_SYMBOL(kstrdup_const);
>>
>> +/**
>> + * devm_kstrdup_const - resource managed conditional string duplication
>> + * @dev: device for which to duplicate the string
>> + * @s: the string to duplicate
>> + * @gfp: the GFP mask used in the kmalloc() call when allocating memory
>> + *
>> + * Function returns source string if it is in .rodata section otherwise it
>> + * fallbacks to devm_kstrdup.
>
> Please make it proper "Returns:" description and move to the end of the
> comment. See Documentation/doc-guide/kernel-doc.rst.
>

Sure.

>> + * Strings allocated by devm_kstrdup_const will be automatically freed when
>> + * the associated device is detached.
>> + */
>> +char *devm_kstrdup_const(struct device *dev, const char *s, gfp_t gfp)
>> +{
>> +     if (is_kernel_rodata((unsigned long)s))
>> +             return s;
>> +
>> +     return devm_kstrdup(dev, s, gfp);
>> +}
>> +EXPORT_SYMBOL(devm_kstrdup_const);
>> +
>
> The devm_ variants seem to belong to drivers/base/devres.c rather than
> mm/util.c
>

Not all devm_ variants live in drivers/base/devres.c, many subsystems
implement them locally. In this case we need to choose between
exporting is_kernel_rodata() and putting devm_kstrdup_const() in
mm/util.c. I chose the latter, since it's cleaner.

Bart

>>  /**
>>   * kstrndup - allocate space for and copy an existing string
>>   * @s: the string to duplicate
>> --
>> 2.18.0
>>
>
> --
> Sincerely yours,
> Mike.
>

Re: [PATCH 1/2] devres: provide devm_kstrdup_const()

[Mike Rapoport]

On Mon, Aug 27, 2018 at 04:28:55PM +0200, Bartosz Golaszewski wrote:
> 2018-08-27 12:33 GMT+02:00 Mike Rapoport <rppt@linux.vnet.ibm.com>:
> > On Mon, Aug 27, 2018 at 10:21:00AM +0200, Bartosz Golaszewski wrote:
> >> Provide a resource managed version of kstrdup_const(). This variant
> >> internally calls devm_kstrdup() on pointers that are outside of
> >> .rodata section. Also provide a corresponding version of devm_kfree().
> >>
> >> Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
> >> ---
> >>  include/linux/device.h |  2 ++
> >>  mm/util.c              | 35 +++++++++++++++++++++++++++++++++++
> >>  2 files changed, 37 insertions(+)
> >>
> >> diff --git a/include/linux/device.h b/include/linux/device.h
> >> index 8f882549edee..f8f5982d26b2 100644
> >> --- a/include/linux/device.h
> >> +++ b/include/linux/device.h
> >> @@ -693,7 +693,9 @@ static inline void *devm_kcalloc(struct device *dev,
> >>       return devm_kmalloc_array(dev, n, size, flags | __GFP_ZERO);
> >>  }
> >>  extern void devm_kfree(struct device *dev, void *p);
> >> +extern void devm_kfree_const(struct device *dev, void *p);
> >>  extern char *devm_kstrdup(struct device *dev, const char *s, gfp_t gfp) __malloc;
> >> +extern char *devm_kstrdup_const(struct device *dev, const char *s, gfp_t gfp);
> >>  extern void *devm_kmemdup(struct device *dev, const void *src, size_t len,
> >>                         gfp_t gfp);
> >>
> >> diff --git a/mm/util.c b/mm/util.c
> >> index d2890a407332..6d1f41b5775e 100644
> >> --- a/mm/util.c
> >> +++ b/mm/util.c

[ ... ]

> >> + * Strings allocated by devm_kstrdup_const will be automatically freed when
> >> + * the associated device is detached.
> >> + */
> >> +char *devm_kstrdup_const(struct device *dev, const char *s, gfp_t gfp)
> >> +{
> >> +     if (is_kernel_rodata((unsigned long)s))
> >> +             return s;
> >> +
> >> +     return devm_kstrdup(dev, s, gfp);
> >> +}
> >> +EXPORT_SYMBOL(devm_kstrdup_const);
> >> +
> >
> > The devm_ variants seem to belong to drivers/base/devres.c rather than
> > mm/util.c
> >
> 
> Not all devm_ variants live in drivers/base/devres.c, many subsystems
> implement them locally. In this case we need to choose between
> exporting is_kernel_rodata() and putting devm_kstrdup_const() in
> mm/util.c. I chose the latter, since it's cleaner.

I rather think that moving is_kernel_rodata() to
include/asm-generic/sections.h and having devm_kstrdup_const() next to
devm_kstrdup() would be cleaner.
 
> Bart
> 

-- 
Sincerely yours,
Mike.

Re: [PATCH 1/2] devres: provide devm_kstrdup_const()

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 2068 bytes --]

Hi Bartosz,

I love your patch! Perhaps something to improve:

[auto build test WARNING on clk/clk-next]
[also build test WARNING on v4.19-rc1 next-20180827]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Bartosz-Golaszewski/devres-provide-devm_kstrdup_const/20180827-162336
base:   https://git.kernel.org/pub/scm/linux/kernel/git/clk/linux.git clk-next
config: powerpc-mpc836x_mds_defconfig (attached as .config)
compiler: powerpc-linux-gnu-gcc (Debian 7.2.0-11) 7.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.2.0 make.cross ARCH=powerpc 

All warnings (new ones prefixed by >>):

   mm/util.c: In function 'devm_kstrdup_const':
>> mm/util.c:110:10: warning: return discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
      return s;
             ^

vim +/const +110 mm/util.c

    94	
    95	/**
    96	 * devm_kstrdup_const - resource managed conditional string duplication
    97	 * @dev: device for which to duplicate the string
    98	 * @s: the string to duplicate
    99	 * @gfp: the GFP mask used in the kmalloc() call when allocating memory
   100	 *
   101	 * Function returns source string if it is in .rodata section otherwise it
   102	 * fallbacks to devm_kstrdup.
   103	 *
   104	 * Strings allocated by devm_kstrdup_const will be automatically freed when
   105	 * the associated device is detached.
   106	 */
   107	char *devm_kstrdup_const(struct device *dev, const char *s, gfp_t gfp)
   108	{
   109		if (is_kernel_rodata((unsigned long)s))
 > 110			return s;
   111	
   112		return devm_kstrdup(dev, s, gfp);
   113	}
   114	EXPORT_SYMBOL(devm_kstrdup_const);
   115	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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