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
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
On Thu, Nov 25, 2010 at 7:01 AM, Julia Lawall <[email protected]> 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
On Thu, 25 Nov 2010, Corentin Chary wrote:
> On Thu, Nov 25, 2010 at 7:01 AM, Julia Lawall <[email protected]> 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
>
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 <[email protected]> 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