debugfs_create_dir return value in acer-wmi, intel_ips and ec_sys

debugfs_create_dir return value in acer-wmi, intel_ips and ec_sys

[Corentin Chary]

Hi,

I was checking debugfs code in platform/x86, because I want to add
some files to eeepc-wmi. And I found something disturbing.

The documentation says:

> This call, if successful, will make a directory called name underneath the
> indicated parent directory.  If parent is NULL, the directory will be
> created in the debugfs root.  On success, the return value is a struct
> dentry pointer which can be used to create files in the directory (and to
> clean it up at the end).  A NULL return value indicates that something went
> wrong.  If ERR_PTR(-ENODEV) is returned, that is an indication that the
> kernel has been built without debugfs support and none of the functions
> described below will work.

But then, here is the code in acer-wmi:

> static void remove_debugfs(void)
> {
>       debugfs_remove(interface->debug.devices);
>       debugfs_remove(interface->debug.root);
> }
>
> static int create_debugfs(void)
> {
>        interface->debug.root = debugfs_create_dir("acer-wmi", NULL);
>        if (!interface->debug.root) {
>                printk(ACER_ERR "Failed to create debugfs directory");
>                return -ENOMEM;
>        }

this code is *not* inside #ifndef CONFIG_DEBUG_FS, so debugfs_create_dir
can return ERR_PTR(-ENODEV) right ?

Then, remove_debug() will call debugfs_remove(ERR_PTR(-ENODEV)) right ?

So, acpi-wmi seems to have an issue when debugfs is disabled, that's "ok".

But then I took a look at intel_ips :

>        ips->debug_root = debugfs_create_dir("ips", NULL);
>        if (!ips->debug_root) {
>                dev_err(&ips->dev->dev,
>                        "failed to create debugfs entries: %ld\n",
>                        PTR_ERR(ips->debug_root));
>                return;
>        }

Then PTR_ERR thing is strange, because ips->debug_root can only be NULL 
here...
But here, it's ok to only check NULL, because it's inside #ifndef 
CONFIG_DEBUG_FS.

So, two drivers checked, to weird error handling code. I did a quick grep and 
opened
the first result: ec_sys.c.

ec_sys.c depends on CONFIG_ACPI_EC_DEBUGFS but doesn't depend on
CONFIG_DEBUG_FS.

Here, again, the code only check for != NULL while it could be ERR_PTR(-
ENODEV):

>        if (ec_device_count == 0) {
>                acpi_ec_debugfs_dir = debugfs_create_dir("ec", NULL);
>                if (!acpi_ec_debugfs_dir)
>                        return -ENOMEM;
>        }
>
>        sprintf(name, "ec%u", ec_device_count);
>        dev_dir = debugfs_create_dir(name, acpi_ec_debugfs_dir);

Here, acpi_ec_debugfs_dir (that can be an invalid pointer) is used as
a parent dentry, and will be dereferenced without checks.

I am missing something obvious, or are most of debugfs implementation
broken when debugfs is disabled ?

Julia, if I am right, coccinelle could help us right ? Can the tool check
if the code is between #ifdef CONFIG_DEBUGS_FS ? That would help a lot.

Thanks,
--
Corentin Chary
http://xf.iksaif.net

Re: debugfs_create_dir return value in acer-wmi, intel_ips and ec_sys

[Julia Lawall]

On Thu, 25 Nov 2010, Corentin Chary wrote:

> Hi,
> 
> I was checking debugfs code in platform/x86, because I want to add
> some files to eeepc-wmi. And I found something disturbing.
> 
> The documentation says:
> 
> > This call, if successful, will make a directory called name underneath the
> > indicated parent directory.  If parent is NULL, the directory will be
> > created in the debugfs root.  On success, the return value is a struct
> > dentry pointer which can be used to create files in the directory (and to
> > clean it up at the end).  A NULL return value indicates that something went
> > wrong.  If ERR_PTR(-ENODEV) is returned, that is an indication that the
> > kernel has been built without debugfs support and none of the functions
> > described below will work.
> 
> But then, here is the code in acer-wmi:
> 
> > static void remove_debugfs(void)
> > {
> >       debugfs_remove(interface->debug.devices);
> >       debugfs_remove(interface->debug.root);
> > }
> >
> > static int create_debugfs(void)
> > {
> >        interface->debug.root = debugfs_create_dir("acer-wmi", NULL);
> >        if (!interface->debug.root) {
> >                printk(ACER_ERR "Failed to create debugfs directory");
> >                return -ENOMEM;
> >        }
> 
> this code is *not* inside #ifndef CONFIG_DEBUG_FS, so debugfs_create_dir
> can return ERR_PTR(-ENODEV) right ?
> 
> Then, remove_debug() will call debugfs_remove(ERR_PTR(-ENODEV)) right ?
> 
> So, acpi-wmi seems to have an issue when debugfs is disabled, that's "ok".
> 
> But then I took a look at intel_ips :
> 
> >        ips->debug_root = debugfs_create_dir("ips", NULL);
> >        if (!ips->debug_root) {
> >                dev_err(&ips->dev->dev,
> >                        "failed to create debugfs entries: %ld\n",
> >                        PTR_ERR(ips->debug_root));
> >                return;
> >        }
> 
> Then PTR_ERR thing is strange, because ips->debug_root can only be NULL 
> here...
> But here, it's ok to only check NULL, because it's inside #ifndef 
> CONFIG_DEBUG_FS.
> 
> So, two drivers checked, to weird error handling code. I did a quick grep and 
> opened
> the first result: ec_sys.c.
> 
> ec_sys.c depends on CONFIG_ACPI_EC_DEBUGFS but doesn't depend on
> CONFIG_DEBUG_FS.
> 
> Here, again, the code only check for != NULL while it could be ERR_PTR(-
> ENODEV):
> 
> >        if (ec_device_count == 0) {
> >                acpi_ec_debugfs_dir = debugfs_create_dir("ec", NULL);
> >                if (!acpi_ec_debugfs_dir)
> >                        return -ENOMEM;
> >        }
> >
> >        sprintf(name, "ec%u", ec_device_count);
> >        dev_dir = debugfs_create_dir(name, acpi_ec_debugfs_dir);
> 
> Here, acpi_ec_debugfs_dir (that can be an invalid pointer) is used as
> a parent dentry, and will be dereferenced without checks.
> 
> I am missing something obvious, or are most of debugfs implementation
> broken when debugfs is disabled ?
> 
> Julia, if I am right, coccinelle could help us right ? Can the tool check
> if the code is between #ifdef CONFIG_DEBUGS_FS ? That would help a lot.

Unfortunately, at the moment, it can't; there is no matching on #ifdefs.  
Perhaps it could be added.

I wonder though if sometimes returning NULL and sometimes returning 
ERR_PTR is something that should be encouraged?  Would one rather convert 
the NULL case to a specific ERR_PTR case?

julia

Re: debugfs_create_dir return value in acer-wmi, intel_ips and ec_sys

[Corentin Chary]

On Thu, Nov 25, 2010 at 7:01 AM, Julia Lawall <julia@diku.dk> wrote:
> On Thu, 25 Nov 2010, Corentin Chary wrote:
>
>> Hi,
>>
>> I was checking debugfs code in platform/x86, because I want to add
>> some files to eeepc-wmi. And I found something disturbing.
>>
>> The documentation says:
>>
>> > This call, if successful, will make a directory called name underneath the
>> > indicated parent directory.  If parent is NULL, the directory will be
>> > created in the debugfs root.  On success, the return value is a struct
>> > dentry pointer which can be used to create files in the directory (and to
>> > clean it up at the end).  A NULL return value indicates that something went
>> > wrong.  If ERR_PTR(-ENODEV) is returned, that is an indication that the
>> > kernel has been built without debugfs support and none of the functions
>> > described below will work.
>>
>> But then, here is the code in acer-wmi:
>>
>> > static void remove_debugfs(void)
>> > {
>> >       debugfs_remove(interface->debug.devices);
>> >       debugfs_remove(interface->debug.root);
>> > }
>> >
>> > static int create_debugfs(void)
>> > {
>> >        interface->debug.root = debugfs_create_dir("acer-wmi", NULL);
>> >        if (!interface->debug.root) {
>> >                printk(ACER_ERR "Failed to create debugfs directory");
>> >                return -ENOMEM;
>> >        }
>>
>> this code is *not* inside #ifndef CONFIG_DEBUG_FS, so debugfs_create_dir
>> can return ERR_PTR(-ENODEV) right ?
>>
>> Then, remove_debug() will call debugfs_remove(ERR_PTR(-ENODEV)) right ?
>>
>> So, acpi-wmi seems to have an issue when debugfs is disabled, that's "ok".
>>
>> But then I took a look at intel_ips :
>>
>> >        ips->debug_root = debugfs_create_dir("ips", NULL);
>> >        if (!ips->debug_root) {
>> >                dev_err(&ips->dev->dev,
>> >                        "failed to create debugfs entries: %ld\n",
>> >                        PTR_ERR(ips->debug_root));
>> >                return;
>> >        }
>>
>> Then PTR_ERR thing is strange, because ips->debug_root can only be NULL
>> here...
>> But here, it's ok to only check NULL, because it's inside #ifndef
>> CONFIG_DEBUG_FS.
>>
>> So, two drivers checked, to weird error handling code. I did a quick grep and
>> opened
>> the first result: ec_sys.c.
>>
>> ec_sys.c depends on CONFIG_ACPI_EC_DEBUGFS but doesn't depend on
>> CONFIG_DEBUG_FS.
>>
>> Here, again, the code only check for != NULL while it could be ERR_PTR(-
>> ENODEV):
>>
>> >        if (ec_device_count == 0) {
>> >                acpi_ec_debugfs_dir = debugfs_create_dir("ec", NULL);
>> >                if (!acpi_ec_debugfs_dir)
>> >                        return -ENOMEM;
>> >        }
>> >
>> >        sprintf(name, "ec%u", ec_device_count);
>> >        dev_dir = debugfs_create_dir(name, acpi_ec_debugfs_dir);
>>
>> Here, acpi_ec_debugfs_dir (that can be an invalid pointer) is used as
>> a parent dentry, and will be dereferenced without checks.
>>
>> I am missing something obvious, or are most of debugfs implementation
>> broken when debugfs is disabled ?

Answer to myself, when debugfs is disabled, it's ok to give broken
dentry pointers to debugfs functions since they won't do anything.

>> Julia, if I am right, coccinelle could help us right ? Can the tool check
>> if the code is between #ifdef CONFIG_DEBUGS_FS ? That would help a lot.
>
> Unfortunately, at the moment, it can't; there is no matching on #ifdefs.
> Perhaps it could be added.

Or better, something to check if a macro is defined in a particular contact ?

> I wonder though if sometimes returning NULL and sometimes returning
> ERR_PTR is something that should be encouraged?  Would one rather convert
> the NULL case to a specific ERR_PTR case?

But yeah, I found debugfs API disturbing, but it seems to be done like that to
ease the "debugfs is disabled case".

Thanks,
-- 
Corentin Chary
http://xf.iksaif.net

Re: debugfs_create_dir return value in acer-wmi, intel_ips and ec_sys

[Julia Lawall]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 4329 bytes --]

On Thu, 25 Nov 2010, Corentin Chary wrote:

> On Thu, Nov 25, 2010 at 7:01 AM, Julia Lawall <julia@diku.dk> wrote:
> > On Thu, 25 Nov 2010, Corentin Chary wrote:
> >
> >> Hi,
> >>
> >> I was checking debugfs code in platform/x86, because I want to add
> >> some files to eeepc-wmi. And I found something disturbing.
> >>
> >> The documentation says:
> >>
> >> > This call, if successful, will make a directory called name underneath the
> >> > indicated parent directory.  If parent is NULL, the directory will be
> >> > created in the debugfs root.  On success, the return value is a struct
> >> > dentry pointer which can be used to create files in the directory (and to
> >> > clean it up at the end).  A NULL return value indicates that something went
> >> > wrong.  If ERR_PTR(-ENODEV) is returned, that is an indication that the
> >> > kernel has been built without debugfs support and none of the functions
> >> > described below will work.
> >>
> >> But then, here is the code in acer-wmi:
> >>
> >> > static void remove_debugfs(void)
> >> > {
> >> >       debugfs_remove(interface->debug.devices);
> >> >       debugfs_remove(interface->debug.root);
> >> > }
> >> >
> >> > static int create_debugfs(void)
> >> > {
> >> >        interface->debug.root = debugfs_create_dir("acer-wmi", NULL);
> >> >        if (!interface->debug.root) {
> >> >                printk(ACER_ERR "Failed to create debugfs directory");
> >> >                return -ENOMEM;
> >> >        }
> >>
> >> this code is *not* inside #ifndef CONFIG_DEBUG_FS, so debugfs_create_dir
> >> can return ERR_PTR(-ENODEV) right ?
> >>
> >> Then, remove_debug() will call debugfs_remove(ERR_PTR(-ENODEV)) right ?
> >>
> >> So, acpi-wmi seems to have an issue when debugfs is disabled, that's "ok".
> >>
> >> But then I took a look at intel_ips :
> >>
> >> >        ips->debug_root = debugfs_create_dir("ips", NULL);
> >> >        if (!ips->debug_root) {
> >> >                dev_err(&ips->dev->dev,
> >> >                        "failed to create debugfs entries: %ld\n",
> >> >                        PTR_ERR(ips->debug_root));
> >> >                return;
> >> >        }
> >>
> >> Then PTR_ERR thing is strange, because ips->debug_root can only be NULL
> >> here...
> >> But here, it's ok to only check NULL, because it's inside #ifndef
> >> CONFIG_DEBUG_FS.
> >>
> >> So, two drivers checked, to weird error handling code. I did a quick grep and
> >> opened
> >> the first result: ec_sys.c.
> >>
> >> ec_sys.c depends on CONFIG_ACPI_EC_DEBUGFS but doesn't depend on
> >> CONFIG_DEBUG_FS.
> >>
> >> Here, again, the code only check for != NULL while it could be ERR_PTR(-
> >> ENODEV):
> >>
> >> >        if (ec_device_count == 0) {
> >> >                acpi_ec_debugfs_dir = debugfs_create_dir("ec", NULL);
> >> >                if (!acpi_ec_debugfs_dir)
> >> >                        return -ENOMEM;
> >> >        }
> >> >
> >> >        sprintf(name, "ec%u", ec_device_count);
> >> >        dev_dir = debugfs_create_dir(name, acpi_ec_debugfs_dir);
> >>
> >> Here, acpi_ec_debugfs_dir (that can be an invalid pointer) is used as
> >> a parent dentry, and will be dereferenced without checks.
> >>
> >> I am missing something obvious, or are most of debugfs implementation
> >> broken when debugfs is disabled ?
> 
> Answer to myself, when debugfs is disabled, it's ok to give broken
> dentry pointers to debugfs functions since they won't do anything.
> 
> >> Julia, if I am right, coccinelle could help us right ? Can the tool check
> >> if the code is between #ifdef CONFIG_DEBUGS_FS ? That would help a lot.
> >
> > Unfortunately, at the moment, it can't; there is no matching on #ifdefs.
> > Perhaps it could be added.
> 
> Or better, something to check if a macro is defined in a particular contact ?

Actually, Daniel Lohmann's group has been working on analyzing #ifdef's.   
Perhaps they have a solution to this problem?  I have added them to the CC 
list.

julia



> > I wonder though if sometimes returning NULL and sometimes returning
> > ERR_PTR is something that should be encouraged?  Would one rather convert
> > the NULL case to a specific ERR_PTR case?
> 
> But yeah, I found debugfs API disturbing, but it seems to be done like that to
> ease the "debugfs is disabled case".
> 
> Thanks,
> -- 
> Corentin Chary
> http://xf.iksaif.net
> 

Re: debugfs_create_dir return value in acer-wmi, intel_ips and ec_sys

[Reinhard Tartler]

On Thu, Nov 25, 2010 at 11:21:20 (CET), Julia Lawall wrote:

> On Thu, 25 Nov 2010, Corentin Chary wrote:
>
>> On Thu, Nov 25, 2010 at 7:01 AM, Julia Lawall <julia@diku.dk> wrote:
>> > On Thu, 25 Nov 2010, Corentin Chary wrote:
>> >
>> >> Hi,
>> >>
>> >> I was checking debugfs code in platform/x86, because I want to add
>> >> some files to eeepc-wmi. And I found something disturbing.
>> >>
>> >> The documentation says:
>> >>
>> >> > This call, if successful, will make a directory called name underneath the
>> >> > indicated parent directory.  If parent is NULL, the directory will be
>> >> > created in the debugfs root.  On success, the return value is a struct
>> >> > dentry pointer which can be used to create files in the directory (and to
>> >> > clean it up at the end).  A NULL return value indicates that something went
>> >> > wrong.  If ERR_PTR(-ENODEV) is returned, that is an indication that the
>> >> > kernel has been built without debugfs support and none of the functions
>> >> > described below will work.
>> >>
>> >> But then, here is the code in acer-wmi:
>> >>
>> >> > static void remove_debugfs(void)
>> >> > {
>> >> >       debugfs_remove(interface->debug.devices);
>> >> >       debugfs_remove(interface->debug.root);
>> >> > }
>> >> >
>> >> > static int create_debugfs(void)
>> >> > {
>> >> >        interface->debug.root = debugfs_create_dir("acer-wmi", NULL);
>> >> >        if (!interface->debug.root) {
>> >> >                printk(ACER_ERR "Failed to create debugfs directory");
>> >> >                return -ENOMEM;
>> >> >        }
>> >>
>> >> this code is *not* inside #ifndef CONFIG_DEBUG_FS, so debugfs_create_dir
>> >> can return ERR_PTR(-ENODEV) right ?
>> >>
>> >> Then, remove_debug() will call debugfs_remove(ERR_PTR(-ENODEV)) right ?
>> >>
>> >> So, acpi-wmi seems to have an issue when debugfs is disabled, that's "ok".
>> >>
>> >> But then I took a look at intel_ips :
>> >>
>> >> >        ips->debug_root = debugfs_create_dir("ips", NULL);
>> >> >        if (!ips->debug_root) {
>> >> >                dev_err(&ips->dev->dev,
>> >> >                        "failed to create debugfs entries: %ld\n",
>> >> >                        PTR_ERR(ips->debug_root));
>> >> >                return;
>> >> >        }
>> >>
>> >> Then PTR_ERR thing is strange, because ips->debug_root can only be NULL
>> >> here...
>> >> But here, it's ok to only check NULL, because it's inside #ifndef
>> >> CONFIG_DEBUG_FS.
>> >>
>> >> So, two drivers checked, to weird error handling code. I did a quick grep and
>> >> opened
>> >> the first result: ec_sys.c.
>> >>
>> >> ec_sys.c depends on CONFIG_ACPI_EC_DEBUGFS but doesn't depend on
>> >> CONFIG_DEBUG_FS.
>> >>
>> >> Here, again, the code only check for != NULL while it could be ERR_PTR(-
>> >> ENODEV):
>> >>
>> >> >        if (ec_device_count == 0) {
>> >> >                acpi_ec_debugfs_dir = debugfs_create_dir("ec", NULL);
>> >> >                if (!acpi_ec_debugfs_dir)
>> >> >                        return -ENOMEM;
>> >> >        }
>> >> >
>> >> >        sprintf(name, "ec%u", ec_device_count);
>> >> >        dev_dir = debugfs_create_dir(name, acpi_ec_debugfs_dir);
>> >>
>> >> Here, acpi_ec_debugfs_dir (that can be an invalid pointer) is used as
>> >> a parent dentry, and will be dereferenced without checks.
>> >>
>> >> I am missing something obvious, or are most of debugfs implementation
>> >> broken when debugfs is disabled ?
>> 
>> Answer to myself, when debugfs is disabled, it's ok to give broken
>> dentry pointers to debugfs functions since they won't do anything.
>> 
>> >> Julia, if I am right, coccinelle could help us right ? Can the tool check
>> >> if the code is between #ifdef CONFIG_DEBUGS_FS ? That would help a lot.
>> >
>> > Unfortunately, at the moment, it can't; there is no matching on #ifdefs.
>> > Perhaps it could be added.
>> 
>> Or better, something to check if a macro is defined in a particular contact ?
>
> Actually, Daniel Lohmann's group has been working on analyzing #ifdef's.   
> Perhaps they have a solution to this problem?  I have added them to the CC 
> list.

Thanks for bringing this thread to our attention, Julia.

We indeed do have a tool that is able to calculate the conditions under
which a line of code is activated or not, taking the constraints from
Kconfig into account. This allows us e.g. to find nested/broken ifdefs
like

#ifndef CONFIG_DEBUG_FS
...
#ifdef CONFIG_DEBUG_FS
#else
#endif
...
#endif

because we are taking kconfig into account, the inner CPP item can also
be some other kconfig item on which CONFIG_DEBUG_FS depends and we would
still find it.

I'm not sure yet how to turn this technique into a tool that would be
helpful to solve this particular problem. Maybe we can integrate this
somehow in coccinelle?

regards,
        Reinhard.

-- 
Gruesse/greetings,
Reinhard Tartler, KeyID 945348A4