debugfs_create_dir return value in acer-wmi, intel_ips and ec_sys

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.

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;
       }

       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;
       }

       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);

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:

Quoted 8 lines

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:

Quoted 6 lines

static void remove_debugfs(void)

{
      debugfs_remove(interface->debug.devices);
      debugfs_remove(interface->debug.root);
}

Quoted 7 lines

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 :

Quoted 7 lines

       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):

Quoted 8 lines

       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.

Quoted 70 lines · 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:

Quoted 8 lines

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:

Quoted 6 lines

static void remove_debugfs(void)
{
      debugfs_remove(interface->debug.devices);
      debugfs_remove(interface->debug.root);
}

Quoted 7 lines

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 :

Quoted 7 lines

       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):

Quoted 6 lines

       if (ec_device_count == 0) {
               acpi_ec_debugfs_dir = debugfs_create_dir("ec", NULL); if (!acpi_ec_debugfs_dir)
                       return -ENOMEM;
       }

Quoted 8 lines

Quoted 2 lines

       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 ?

Quoted 2 lines

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?

Quoted 72 lines · Julia Lawall

Quoted 70 lines · 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:

Quoted 8 lines

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:

Quoted 6 lines

static void remove_debugfs(void)
{
      debugfs_remove(interface->debug.devices);
      debugfs_remove(interface->debug.root);
}

Quoted 7 lines

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 :

Quoted 7 lines

       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):

Quoted 6 lines

       if (ec_device_count == 0) {
               acpi_ec_debugfs_dir = debugfs_create_dir("ec", NULL); if (!acpi_ec_debugfs_dir)
                       return -ENOMEM;
       }

Quoted 8 lines

Quoted 8 lines

Quoted 2 lines

       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.

Quoted 5 lines

Quoted 2 lines

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 ?

Quoted 3 lines

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,

Signature · 2 lines

Corentin Chary
http://xf.iksaif.net

Quoted 88 lines · Corentin Chary

Quoted 72 lines · Julia Lawall

Quoted 70 lines · 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:

Quoted 8 lines

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:

Quoted 6 lines

static void remove_debugfs(void)
{
      debugfs_remove(interface->debug.devices);
      debugfs_remove(interface->debug.root);
}

Quoted 7 lines

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 :

Quoted 7 lines

       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):

Quoted 6 lines

       if (ec_device_count == 0) {
               acpi_ec_debugfs_dir = debugfs_create_dir("ec", NULL); if (!acpi_ec_debugfs_dir)
                       return -ENOMEM;
       }

Quoted 8 lines

Quoted 8 lines

Quoted 2 lines

       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.

Quoted 3 lines

Quoted 2 lines

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.

Quoted 4 lines

Quoted 2 lines

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.