Messages in this thread | | | From | Corentin Chary <> | Subject | debugfs_create_dir return value in acer-wmi, intel_ips and ec_sys | Date | Thu, 25 Nov 2010 00:51:06 +0100 |
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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
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