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Date: Thu, 25 Nov 2010 07:01:22 +0100 (CET) From: Julia Lawall <julia@...u.dk> To: Corentin Chary <corentin.chary@...il.com> Cc: LKML <linux-kernel@...r.kernel.org>, platform-driver-x86@...r.kernel.org, linux acpi <linux-acpi@...r.kernel.org>, Carlos Corbacho <carlos@...angeworlds.co.uk>, Matthew Garrett <mjg@...hat.com>, Axel Lin <axel.lin@...il.com>, Thomas Renninger <trenn@...e.de>, Thomas Renninger <trenn@...e.de> Subject: Re: debugfs_create_dir return value in acer-wmi, intel_ips and ec_sys 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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