module: add debug stats to help identify memory pressure

JIRA: https://issues.redhat.com/browse/RHEL-28063 Conflicts: Adding RHEL-only MODULE_STATS set to n for now. Possibly add in future -debug kernels, to be determined. Add rest of commit(s) to enable clean backport for further commits. commit df3e764d8e5cd416efee29e0de3c93917dff5d33 Author: Luis Chamberlain <mcgrof@kernel.org> Date: Tue Mar 28 20:03:19 2023 -0700 module: add debug stats to help identify memory pressure Loading modules with finit_module() can end up using vmalloc(), vmap() and vmalloc() again, for a total of up to 3 separate allocations in the worst case for a single module. We always kernel_read*() the module, that's a vmalloc(). Then vmap() is used for the module decompression, and if so the last read buffer is freed as we use the now decompressed module buffer to stuff data into our copy module. The last allocation is specific to each architectures but pretty much that's generally a series of vmalloc() calls or a variation of vmalloc to handle ELF sections with special permissions. Evaluation with new stress-ng module support [1] with just 100 ops is proving that you can end up using GiBs of data easily even with all care we have in the kernel and userspace today in trying to not load modules which are already loaded. 100 ops seems to resemble the sort of pressure a system with about 400 CPUs can create on module loading. Although issues relating to duplicate module requests due to each CPU inucurring a new module reuest is silly and some of these are being fixed, we currently lack proper tooling to help diagnose easily what happened, when it happened and who likely is to blame -- userspace or kernel module autoloading. Provide an initial set of stats which use debugfs to let us easily scrape post-boot information about failed loads. This sort of information can be used on production worklaods to try to optimize *avoiding* redundant memory pressure using finit_module(). There's a few examples that can be provided: A 255 vCPU system without the next patch in this series applied: Startup finished in 19.143s (kernel) + 7.078s (userspace) = 26.221s graphical.target reached after 6.988s in userspace And 13.58 GiB of virtual memory space lost due to failed module loading: root@big ~ # cat /sys/kernel/debug/modules/stats Mods ever loaded 67 Mods failed on kread 0 Mods failed on decompress 0 Mods failed on becoming 0 Mods failed on load 1411 Total module size 11464704 Total mod text size 4194304 Failed kread bytes 0 Failed decompress bytes 0 Failed becoming bytes 0 Failed kmod bytes 14588526272 Virtual mem wasted bytes 14588526272 Average mod size 171115 Average mod text size 62602 Average fail load bytes 10339140 Duplicate failed modules: module-name How-many-times Reason kvm_intel 249 Load kvm 249 Load irqbypass 8 Load crct10dif_pclmul 128 Load ghash_clmulni_intel 27 Load sha512_ssse3 50 Load sha512_generic 200 Load aesni_intel 249 Load crypto_simd 41 Load cryptd 131 Load evdev 2 Load serio_raw 1 Load virtio_pci 3 Load nvme 3 Load nvme_core 3 Load virtio_pci_legacy_dev 3 Load virtio_pci_modern_dev 3 Load t10_pi 3 Load virtio 3 Load crc32_pclmul 6 Load crc64_rocksoft 3 Load crc32c_intel 40 Load virtio_ring 3 Load crc64 3 Load The following screen shot, of a simple 8vcpu 8 GiB KVM guest with the next patch in this series applied, shows 226.53 MiB are wasted in virtual memory allocations which due to duplicate module requests during boot. It also shows an average module memory size of 167.10 KiB and an an average module .text + .init.text size of 61.13 KiB. The end shows all modules which were detected as duplicate requests and whether or not they failed early after just the first kernel_read*() call or late after we've already allocated the private space for the module in layout_and_allocate(). A system with module decompression would reveal more wasted virtual memory space. We should put effort now into identifying the source of these duplicate module requests and trimming these down as much possible. Larger systems will obviously show much more wasted virtual memory allocations. root@kmod ~ # cat /sys/kernel/debug/modules/stats Mods ever loaded 67 Mods failed on kread 0 Mods failed on decompress 0 Mods failed on becoming 83 Mods failed on load 16 Total module size 11464704 Total mod text size 4194304 Failed kread bytes 0 Failed decompress bytes 0 Failed becoming bytes 228959096 Failed kmod bytes 8578080 Virtual mem wasted bytes 237537176 Average mod size 171115 Average mod text size 62602 Avg fail becoming bytes 2758544 Average fail load bytes 536130 Duplicate failed modules: module-name How-many-times Reason kvm_intel 7 Becoming kvm 7 Becoming irqbypass 6 Becoming & Load crct10dif_pclmul 7 Becoming & Load ghash_clmulni_intel 7 Becoming & Load sha512_ssse3 6 Becoming & Load sha512_generic 7 Becoming & Load aesni_intel 7 Becoming crypto_simd 7 Becoming & Load cryptd 3 Becoming & Load evdev 1 Becoming serio_raw 1 Becoming nvme 3 Becoming nvme_core 3 Becoming t10_pi 3 Becoming virtio_pci 3 Becoming crc32_pclmul 6 Becoming & Load crc64_rocksoft 3 Becoming crc32c_intel 3 Becoming virtio_pci_modern_dev 2 Becoming virtio_pci_legacy_dev 1 Becoming crc64 2 Becoming virtio 2 Becoming virtio_ring 2 Becoming [0] https://github.com/ColinIanKing/stress-ng.git [1] echo 0 > /proc/sys/vm/oom_dump_tasks ./stress-ng --module 100 --module-name xfs Signed-off-by: Luis Chamberlain <mcgrof@kernel.org> Signed-off-by: Donald Dutile <ddutile@redhat.com>
2026-09-09 00:08:12 +08:00 · 2024-06-17 14:17:25 -04:00
parent 5d28ce51db
commit e41f7154cf
10 changed files with 638 additions and 14 deletions
@@ -216,12 +216,30 @@ relay interface
 Module Support
 ==============

-Module Loading
--------------
+Kernel module auto-loading
+--------------------------

-.. kernel-doc:: kernel/kmod.c
+.. kernel-doc:: kernel/module/kmod.c
   :export:

+Module debugging
+----------------
+
+.. kernel-doc:: kernel/module/stats.c
+   :doc: module debugging statistics overview
+
+dup_failed_modules - tracks duplicate failed modules
+****************************************************
+
+.. kernel-doc:: kernel/module/stats.c
+   :doc: dup_failed_modules - tracks duplicate failed modules
+
+module statistics debugfs counters
+**********************************
+
+.. kernel-doc:: kernel/module/stats.c
+   :doc: module statistics debugfs counters
+
 Inter Module support
 --------------------

@@ -22,6 +22,45 @@ menuconfig MODULES

 if MODULES

+config MODULE_DEBUGFS
+	bool
+
+config MODULE_DEBUG
+	bool "Module debugging"
+	depends on DEBUG_FS
+	help
+	  Allows you to enable / disable features which can help you debug
+	  modules. You don't need these options on production systems.
+
+if MODULE_DEBUG
+
+config MODULE_STATS
+	bool "Module statistics"
+	depends on DEBUG_FS
+	select MODULE_DEBUGFS
+	help
+	  This option allows you to maintain a record of module statistics.
+	  For example, size of all modules, average size, text size, a list
+	  of failed modules and the size for each of those. For failed
+	  modules we keep track of modules which failed due to either the
+	  existing module taking too long to load or that module was already
+	  loaded.
+
+	  You should enable this if you are debugging production loads
+	  and want to see if userspace or the kernel is doing stupid things
+	  with loading modules when it shouldn't or if you want to help
+	  optimize userspace / kernel space module autoloading schemes.
+	  You might want to do this because failed modules tend to use
+	  up significant amount of memory, and so you'd be doing everyone a
+	  favor in avoiding these failures proactively.
+
+	  This functionality is also useful for those experimenting with
+	  module .text ELF section optimization.
+
+	  If unsure, say N.
+
+endif # MODULE_DEBUG
+
 config MODULE_FORCE_LOAD
 	bool "Forced module loading"
 	default n
@@ -51,7 +90,7 @@ config MODULE_FORCE_UNLOAD
 config MODULE_UNLOAD_TAINT_TRACKING
 	bool "Tainted module unload tracking"
 	depends on MODULE_UNLOAD
-	default n
+	select MODULE_DEBUGFS
 	help
 	  This option allows you to maintain a record of each unloaded
 	  module that tainted the kernel. In addition to displaying a
@@ -21,3 +21,4 @@ obj-$(CONFIG_SYSFS) += sysfs.o
 obj-$(CONFIG_KGDB_KDB) += kdb.o
 obj-$(CONFIG_MODVERSIONS) += version.o
 obj-$(CONFIG_MODULE_UNLOAD_TAINT_TRACKING) += tracking.o
+obj-$(CONFIG_MODULE_STATS) += stats.o
@@ -297,6 +297,10 @@ int module_decompress(struct load_info *info, const void *buf, size_t size)
 	ssize_t data_size;
 	int error;

+#if defined(CONFIG_MODULE_STATS)
+	info->compressed_len = size;
+#endif
+
 	/*
 	 * Start with number of pages twice as big as needed for
 	 * compressed data.
@@ -59,6 +59,9 @@ struct load_info {
 	unsigned long mod_kallsyms_init_off;
 #endif
 #ifdef CONFIG_MODULE_DECOMPRESS
+#ifdef CONFIG_MODULE_STATS
+	unsigned long compressed_len;
+#endif
 	struct page **pages;
 	unsigned int max_pages;
 	unsigned int used_pages;
@@ -143,6 +146,81 @@ static inline bool set_livepatch_module(struct module *mod)
 #endif
 }

+/**
+ * enum fail_dup_mod_reason - state at which a duplicate module was detected
+ *
+ * @FAIL_DUP_MOD_BECOMING: the module is read properly, passes all checks but
+ * 	we've determined that another module with the same name is already loaded
+ * 	or being processed on our &modules list. This happens on early_mod_check()
+ * 	right before layout_and_allocate(). The kernel would have already
+ * 	vmalloc()'d space for the entire module through finit_module(). If
+ * 	decompression was used two vmap() spaces were used. These failures can
+ * 	happen when userspace has not seen the module present on the kernel and
+ * 	tries to load the module multiple times at same time.
+ * @FAIL_DUP_MOD_LOAD: the module has been read properly, passes all validation
+ *	checks and the kernel determines that the module was unique and because
+ *	of this allocated yet another private kernel copy of the module space in
+ *	layout_and_allocate() but after this determined in add_unformed_module()
+ *	that another module with the same name is already loaded or being processed.
+ *	These failures should be mitigated as much as possible and are indicative
+ *	of really fast races in loading modules. Without module decompression
+ *	they waste twice as much vmap space. With module decompression three
+ *	times the module's size vmap space is wasted.
+ */
+enum fail_dup_mod_reason {
+	FAIL_DUP_MOD_BECOMING = 0,
+	FAIL_DUP_MOD_LOAD,
+};
+
+#ifdef CONFIG_MODULE_DEBUGFS
+extern struct dentry *mod_debugfs_root;
+#endif
+
+#ifdef CONFIG_MODULE_STATS
+
+#define mod_stat_add_long(count, var) atomic_long_add(count, var)
+#define mod_stat_inc(name) atomic_inc(name)
+
+extern atomic_long_t total_mod_size;
+extern atomic_long_t total_text_size;
+extern atomic_long_t invalid_kread_bytes;
+extern atomic_long_t invalid_decompress_bytes;
+
+extern atomic_t modcount;
+extern atomic_t failed_kreads;
+extern atomic_t failed_decompress;
+struct mod_fail_load {
+	struct list_head list;
+	char name[MODULE_NAME_LEN];
+	atomic_long_t count;
+	unsigned long dup_fail_mask;
+};
+
+int try_add_failed_module(const char *name, enum fail_dup_mod_reason reason);
+void mod_stat_bump_invalid(struct load_info *info, int flags);
+void mod_stat_bump_becoming(struct load_info *info, int flags);
+
+#else
+
+#define mod_stat_add_long(name, var)
+#define mod_stat_inc(name)
+
+static inline int try_add_failed_module(const char *name,
+					enum fail_dup_mod_reason reason)
+{
+	return 0;
+}
+
+static inline void mod_stat_bump_invalid(struct load_info *info, int flags)
+{
+}
+
+static inline void mod_stat_bump_becoming(struct load_info *info, int flags)
+{
+}
+
+#endif /* CONFIG_MODULE_STATS */
+
 #ifdef CONFIG_MODULE_UNLOAD_TAINT_TRACKING
 struct mod_unload_taint {
 	struct list_head list;
@@ -55,6 +55,7 @@
 #include <linux/bsearch.h>
 #include <linux/dynamic_debug.h>
 #include <linux/audit.h>
+#include <linux/debugfs.h>
 #include <uapi/linux/module.h>
 #include "internal.h"

@@ -2501,6 +2502,18 @@ static noinline int do_init_module(struct module *mod)
 {
 	int ret = 0;
 	struct mod_initfree *freeinit;
+#if defined(CONFIG_MODULE_STATS)
+	unsigned int text_size = 0, total_size = 0;
+
+	for_each_mod_mem_type(type) {
+		const struct module_memory *mod_mem = &mod->mem[type];
+		if (mod_mem->size) {
+			total_size += mod_mem->size;
+			if (type == MOD_TEXT || type == MOD_INIT_TEXT)
+				text_size += mod_mem->size;
+		}
+	}
+#endif

 	freeinit = kmalloc(sizeof(*freeinit), GFP_KERNEL);
 	if (!freeinit) {
@@ -2562,6 +2575,7 @@ static noinline int do_init_module(struct module *mod)
 		mod->mem[type].base = NULL;
 		mod->mem[type].size = 0;
 	}
+
 #ifdef CONFIG_DEBUG_INFO_BTF_MODULES
 	/* .BTF is not SHF_ALLOC and will get removed, so sanitize pointer */
 	mod->btf_data = NULL;
@@ -2585,6 +2599,11 @@ static noinline int do_init_module(struct module *mod)
 	mutex_unlock(&module_mutex);
 	wake_up_all(&module_wq);

+	mod_stat_add_long(text_size, &total_text_size);
+	mod_stat_add_long(total_size, &total_mod_size);
+
+	mod_stat_inc(&modcount);
+
 	return 0;

 fail_free_freeinit:
@@ -2600,6 +2619,7 @@ fail:
 	ftrace_release_mod(mod);
 	free_module(mod);
 	wake_up_all(&module_wq);
+
 	return ret;
 }

@@ -2633,7 +2653,8 @@ static bool finished_loading(const char *name)
 }

 /* Must be called with module_mutex held */
-static int module_patient_check_exists(const char *name)
+static int module_patient_check_exists(const char *name,
+				       enum fail_dup_mod_reason reason)
 {
 	struct module *old;
 	int err = 0;
@@ -2656,6 +2677,9 @@ static int module_patient_check_exists(const char *name)
 		old = find_module_all(name, strlen(name), true);
 	}

+	if (try_add_failed_module(name, reason))
+		pr_warn("Could not add fail-tracking for module: %s\n", name);
+
 	/*
 	 * We are here only when the same module was being loaded. Do
 	 * not try to load it again right now. It prevents long delays
@@ -2680,7 +2704,7 @@ static int add_unformed_module(struct module *mod)
 	mod->state = MODULE_STATE_UNFORMED;

 	mutex_lock(&module_mutex);
-	err = module_patient_check_exists(mod->name);
+	err = module_patient_check_exists(mod->name, FAIL_DUP_MOD_LOAD);
 	if (err)
 		goto out;

@@ -2802,6 +2826,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
 		       int flags)
 {
 	struct module *mod;
+	bool module_allocated = false;
 	long err = 0;
 	char *after_dashes;

@@ -2846,6 +2871,8 @@ static int load_module(struct load_info *info, const char __user *uargs,
 		goto free_copy;
 	}

+	module_allocated = true;
+
 	audit_log_kern_module(mod->name);

 	/* Reserve our place in the list. */
@@ -2993,6 +3020,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
 	synchronize_rcu();
 	mutex_unlock(&module_mutex);
 free_module:
+	mod_stat_bump_invalid(info, flags);
 	/* Free lock-classes; relies on the preceding sync_rcu() */
 	for_class_mod_mem_type(type, core_data) {
 		lockdep_free_key_range(mod->mem[type].base,
@@ -3001,6 +3029,13 @@ static int load_module(struct load_info *info, const char __user *uargs,

 	module_deallocate(mod, info);
 free_copy:
+	/*
+	 * The info->len is always set. We distinguish between
+	 * failures once the proper module was allocated and
+	 * before that.
+	 */
+	if (!module_allocated)
+		mod_stat_bump_becoming(info, flags);
 	free_copy(info, flags);
 	return err;
 }
@@ -3019,8 +3054,11 @@ SYSCALL_DEFINE3(init_module, void __user *, umod,
 	       umod, len, uargs);

 	err = copy_module_from_user(umod, len, &info);
-	if (err)
+	if (err) {
+		mod_stat_inc(&failed_kreads);
+		mod_stat_add_long(len, &invalid_kread_bytes);
 		return err;
+	}

 	return load_module(&info, uargs, 0);
 }
@@ -3045,14 +3083,20 @@ SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags)

 	len = kernel_read_file_from_fd(fd, 0, &buf, INT_MAX, NULL,
 				       READING_MODULE);
-	if (len < 0)
+	if (len < 0) {
+		mod_stat_inc(&failed_kreads);
+		mod_stat_add_long(len, &invalid_kread_bytes);
 		return len;
+	}

 	if (flags & MODULE_INIT_COMPRESSED_FILE) {
 		err = module_decompress(&info, buf, len);
 		vfree(buf); /* compressed data is no longer needed */
-		if (err)
+		if (err) {
+			mod_stat_inc(&failed_decompress);
+			mod_stat_add_long(len, &invalid_decompress_bytes);
 			return err;
+		}
 	} else {
 		info.hdr = buf;
 		info.len = len;
@@ -3252,3 +3296,14 @@ void print_modules(void)
 			last_unloaded_module.taints);
 	pr_cont("\n");
 }
+
+#ifdef CONFIG_MODULE_DEBUGFS
+struct dentry *mod_debugfs_root;
+
+static int module_debugfs_init(void)
+{
+	mod_debugfs_root = debugfs_create_dir("modules", NULL);
+	return 0;
+}
+module_init(module_debugfs_init);
+#endif
@@ -0,0 +1,430 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Debugging module statistics.
+ *
+ * Copyright (C) 2023 Luis Chamberlain <mcgrof@kernel.org>
+ */
+
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/printk.h>
+#include <linux/slab.h>
+#include <linux/list.h>
+#include <linux/debugfs.h>
+#include <linux/rculist.h>
+#include <linux/math.h>
+
+#include "internal.h"
+
+/**
+ * DOC: module debugging statistics overview
+ *
+ * Enabling CONFIG_MODULE_STATS enables module debugging statistics which
+ * are useful to monitor and root cause memory pressure issues with module
+ * loading. These statistics are useful to allow us to improve production
+ * workloads.
+ *
+ * The current module debugging statistics supported help keep track of module
+ * loading failures to enable improvements either for kernel module auto-loading
+ * usage (request_module()) or interactions with userspace. Statistics are
+ * provided to track all possible failures in the finit_module() path and memory
+ * wasted in this process space.  Each of the failure counters are associated
+ * to a type of module loading failure which is known to incur a certain amount
+ * of memory allocation loss. In the worst case loading a module will fail after
+ * a 3 step memory allocation process:
+ *
+ *   a) memory allocated with kernel_read_file_from_fd()
+ *   b) module decompression processes the file read from
+ *      kernel_read_file_from_fd(), and vmap() is used to map
+ *      the decompressed module to a new local buffer which represents
+ *      a copy of the decompressed module passed from userspace. The buffer
+ *      from kernel_read_file_from_fd() is freed right away.
+ *   c) layout_and_allocate() allocates space for the final resting
+ *      place where we would keep the module if it were to be processed
+ *      successfully.
+ *
+ * If a failure occurs after these three different allocations only one
+ * counter will be incremented with the summation of the allocated bytes freed
+ * incurred during this failure. Likewise, if module loading failed only after
+ * step b) a separate counter is used and incremented for the bytes freed and
+ * not used during both of those allocations.
+ *
+ * Virtual memory space can be limited, for example on x86 virtual memory size
+ * defaults to 128 MiB. We should strive to limit and avoid wasting virtual
+ * memory allocations when possible. These module debugging statistics help
+ * to evaluate how much memory is being wasted on bootup due to module loading
+ * failures.
+ *
+ * All counters are designed to be incremental. Atomic counters are used so to
+ * remain simple and avoid delays and deadlocks.
+ */
+
+/**
+ * DOC: dup_failed_modules - tracks duplicate failed modules
+ *
+ * Linked list of modules which failed to be loaded because an already existing
+ * module with the same name was already being processed or already loaded.
+ * The finit_module() system call incurs heavy virtual memory allocations. In
+ * the worst case an finit_module() system call can end up allocating virtual
+ * memory 3 times:
+ *
+ *   1) kernel_read_file_from_fd() call uses vmalloc()
+ *   2) optional module decompression uses vmap()
+ *   3) layout_and allocate() can use vzalloc() or an arch specific variation of
+ *      vmalloc to deal with ELF sections requiring special permissions
+ *
+ * In practice on a typical boot today most finit_module() calls fail due to
+ * the module with the same name already being loaded or about to be processed.
+ * All virtual memory allocated to these failed modules will be freed with
+ * no functional use.
+ *
+ * To help with this the dup_failed_modules allows us to track modules which
+ * failed to load due to the fact that a module was already loaded or being
+ * processed.  There are only two points at which we can fail such calls,
+ * we list them below along with the number of virtual memory allocation
+ * calls:
+ *
+ *   a) FAIL_DUP_MOD_BECOMING: at the end of early_mod_check() before
+ *	layout_and_allocate(). This does not yet happen.
+ *	- with module decompression: 2 virtual memory allocation calls
+ *	- without module decompression: 1 virtual memory allocation calls
+ *   b) FAIL_DUP_MOD_LOAD: after layout_and_allocate() on add_unformed_module()
+ *   	- with module decompression 3 virtual memory allocation calls
+ *   	- without module decompression 2 virtual memory allocation calls
+ *
+ * We should strive to get this list to be as small as possible. If this list
+ * is not empty it is a reflection of possible work or optimizations possible
+ * either in-kernel or in userspace.
+ */
+static LIST_HEAD(dup_failed_modules);
+
+/**
+ * DOC: module statistics debugfs counters
+ *
+ * The total amount of wasted virtual memory allocation space during module
+ * loading can be computed by adding the total from the summation:
+ *
+ *   * @invalid_kread_bytes +
+ *     @invalid_decompress_bytes +
+ *     @invalid_becoming_bytes +
+ *     @invalid_mod_bytes
+ *
+ * The following debugfs counters are available to inspect module loading
+ * failures:
+ *
+ *   * total_mod_size: total bytes ever used by all modules we've dealt with on
+ *     this system
+ *   * total_text_size: total bytes of the .text and .init.text ELF section
+ *     sizes we've dealt with on this system
+ *   * invalid_kread_bytes: bytes allocated and then freed on failures which
+ *     happen due to the initial kernel_read_file_from_fd(). kernel_read_file_from_fd()
+ *     uses vmalloc(). These should typically not happen unless your system is
+ *     under memory pressure.
+ *   * invalid_decompress_bytes: number of bytes allocated and freed due to
+ *     memory allocations in the module decompression path that use vmap().
+ *     These typically should not happen unless your system is under memory
+ *     pressure.
+ *   * invalid_becoming_bytes: total number of bytes allocated and freed used
+ *     used to read the kernel module userspace wants us to read before we
+ *     promote it to be processed to be added to our @modules linked list.
+ *     These failures could in theory happen if we had a check in
+ *     between a successful kernel_read_file_from_fd()
+ *     call and right before we allocate the our private memory for the module
+ *     which would be kept if the module is successfully loaded. The most common
+ *     reason for this failure is when userspace is racing to load a module
+ *     which it does not yet see loaded. The first module to succeed in
+ *     add_unformed_module() will add a module to our &modules list and
+ *     subsequent loads of modules with the same name will error out at the
+ *     end of early_mod_check(). A check for module_patient_check_exists()
+ *     at the end of early_mod_check() could be added to prevent duplicate allocations
+ *     on layout_and_allocate() for modules already being processed. These
+ *     duplicate failed modules are non-fatal, however they typically are
+ *     indicative of userspace not seeing a module in userspace loaded yet and
+ *     unnecessarily trying to load a module before the kernel even has a chance
+ *     to begin to process prior requests. Although duplicate failures can be
+ *     non-fatal, we should try to reduce vmalloc() pressure proactively, so
+ *     ideally after boot this will be close to as 0 as possible.  If module
+ *     decompression was used we also add to this counter the cost of the
+ *     initial kernel_read_file_from_fd() of the compressed module. If module
+ *     decompression was not used the value represents the total allocated and
+ *     freed bytes in kernel_read_file_from_fd() calls for these type of
+ *     failures. These failures can occur because:
+ *
+ *    * module_sig_check() - module signature checks
+ *    * elf_validity_cache_copy() - some ELF validation issue
+ *    * early_mod_check():
+ *
+ *      * blacklisting
+ *      * failed to rewrite section headers
+ *      * version magic
+ *      * live patch requirements didn't check out
+ *      * the module was detected as being already present
+ *
+ *   * invalid_mod_bytes: these are the total number of bytes allocated and
+ *     freed due to failures after we did all the sanity checks of the module
+ *     which userspace passed to us and after our first check that the module
+ *     is unique.  A module can still fail to load if we detect the module is
+ *     loaded after we allocate space for it with layout_and_allocate(), we do
+ *     this check right before processing the module as live and run its
+ *     initialization routines. Note that you have a failure of this type it
+ *     also means the respective kernel_read_file_from_fd() memory space was
+ *     also freed and not used, and so we increment this counter with twice
+ *     the size of the module. Additionally if you used module decompression
+ *     the size of the compressed module is also added to this counter.
+ *
+ *  * modcount: how many modules we've loaded in our kernel life time
+ *  * failed_kreads: how many modules failed due to failed kernel_read_file_from_fd()
+ *  * failed_decompress: how many failed module decompression attempts we've had.
+ *    These really should not happen unless your compression / decompression
+ *    might be broken.
+ *  * failed_becoming: how many modules failed after we kernel_read_file_from_fd()
+ *    it and before we allocate memory for it with layout_and_allocate(). This
+ *    counter is never incremented if you manage to validate the module and
+ *    call layout_and_allocate() for it.
+ *  * failed_load_modules: how many modules failed once we've allocated our
+ *    private space for our module using layout_and_allocate(). These failures
+ *    should hopefully mostly be dealt with already. Races in theory could
+ *    still exist here, but it would just mean the kernel had started processing
+ *    two threads concurrently up to early_mod_check() and one thread won.
+ *    These failures are good signs the kernel or userspace is doing something
+ *    seriously stupid or that could be improved. We should strive to fix these,
+ *    but it is perhaps not easy to fix them. A recent example are the modules
+ *    requests incurred for frequency modules, a separate module request was
+ *    being issued for each CPU on a system.
+ */
+
+atomic_long_t total_mod_size;
+atomic_long_t total_text_size;
+atomic_long_t invalid_kread_bytes;
+atomic_long_t invalid_decompress_bytes;
+static atomic_long_t invalid_becoming_bytes;
+static atomic_long_t invalid_mod_bytes;
+atomic_t modcount;
+atomic_t failed_kreads;
+atomic_t failed_decompress;
+static atomic_t failed_becoming;
+static atomic_t failed_load_modules;
+
+static const char *mod_fail_to_str(struct mod_fail_load *mod_fail)
+{
+	if (test_bit(FAIL_DUP_MOD_BECOMING, &mod_fail->dup_fail_mask) &&
+	    test_bit(FAIL_DUP_MOD_LOAD, &mod_fail->dup_fail_mask))
+		return "Becoming & Load";
+	if (test_bit(FAIL_DUP_MOD_BECOMING, &mod_fail->dup_fail_mask))
+		return "Becoming";
+	if (test_bit(FAIL_DUP_MOD_LOAD, &mod_fail->dup_fail_mask))
+		return "Load";
+	return "Bug-on-stats";
+}
+
+void mod_stat_bump_invalid(struct load_info *info, int flags)
+{
+	atomic_long_add(info->len * 2, &invalid_mod_bytes);
+	atomic_inc(&failed_load_modules);
+#if defined(CONFIG_MODULE_DECOMPRESS)
+	if (flags & MODULE_INIT_COMPRESSED_FILE)
+		atomic_long_add(info->compressed_len, &invalid_mod_byte);
+#endif
+}
+
+void mod_stat_bump_becoming(struct load_info *info, int flags)
+{
+	atomic_inc(&failed_becoming);
+	atomic_long_add(info->len, &invalid_becoming_bytes);
+#if defined(CONFIG_MODULE_DECOMPRESS)
+	if (flags & MODULE_INIT_COMPRESSED_FILE)
+		atomic_long_add(info->compressed_len, &invalid_becoming_bytes);
+#endif
+}
+
+int try_add_failed_module(const char *name, enum fail_dup_mod_reason reason)
+{
+	struct mod_fail_load *mod_fail;
+
+	list_for_each_entry_rcu(mod_fail, &dup_failed_modules, list,
+				lockdep_is_held(&module_mutex)) {
+		if (!strcmp(mod_fail->name, name)) {
+			atomic_long_inc(&mod_fail->count);
+			__set_bit(reason, &mod_fail->dup_fail_mask);
+			goto out;
+		}
+	}
+
+	mod_fail = kzalloc(sizeof(*mod_fail), GFP_KERNEL);
+	if (!mod_fail)
+		return -ENOMEM;
+	memcpy(mod_fail->name, name, strlen(name));
+	__set_bit(reason, &mod_fail->dup_fail_mask);
+	atomic_long_inc(&mod_fail->count);
+	list_add_rcu(&mod_fail->list, &dup_failed_modules);
+out:
+	return 0;
+}
+
+/*
+ * At 64 bytes per module and assuming a 1024 bytes preamble we can fit the
+ * 112 module prints within 8k.
+ *
+ * 1024 + (64*112) = 8k
+ */
+#define MAX_PREAMBLE 1024
+#define MAX_FAILED_MOD_PRINT 112
+#define MAX_BYTES_PER_MOD 64
+static ssize_t read_file_mod_stats(struct file *file, char __user *user_buf,
+				   size_t count, loff_t *ppos)
+{
+	struct mod_fail_load *mod_fail;
+	unsigned int len, size, count_failed = 0;
+	char *buf;
+	u32 live_mod_count, fkreads, fdecompress, fbecoming, floads;
+	u64 total_size, text_size, ikread_bytes, ibecoming_bytes, idecompress_bytes, imod_bytes,
+	    total_virtual_lost;
+
+	live_mod_count = atomic_read(&modcount);
+	fkreads = atomic_read(&failed_kreads);
+	fdecompress = atomic_read(&failed_decompress);
+	fbecoming = atomic_read(&failed_becoming);
+	floads = atomic_read(&failed_load_modules);
+
+	total_size = atomic64_read(&total_mod_size);
+	text_size = atomic64_read(&total_text_size);
+	ikread_bytes = atomic64_read(&invalid_kread_bytes);
+	idecompress_bytes = atomic64_read(&invalid_decompress_bytes);
+	ibecoming_bytes = atomic64_read(&invalid_becoming_bytes);
+	imod_bytes = atomic64_read(&invalid_mod_bytes);
+
+	total_virtual_lost = ikread_bytes + idecompress_bytes + ibecoming_bytes + imod_bytes;
+
+	size = MAX_PREAMBLE + min((unsigned int)(floads + fbecoming),
+				  (unsigned int)MAX_FAILED_MOD_PRINT) * MAX_BYTES_PER_MOD;
+	buf = kzalloc(size, GFP_KERNEL);
+	if (buf == NULL)
+		return -ENOMEM;
+
+	/* The beginning of our debug preamble */
+	len = scnprintf(buf + 0, size - len, "%25s\t%u\n", "Mods ever loaded", live_mod_count);
+
+	len += scnprintf(buf + len, size - len, "%25s\t%u\n", "Mods failed on kread", fkreads);
+
+	len += scnprintf(buf + len, size - len, "%25s\t%u\n", "Mods failed on decompress",
+			 fdecompress);
+	len += scnprintf(buf + len, size - len, "%25s\t%u\n", "Mods failed on becoming", fbecoming);
+
+	len += scnprintf(buf + len, size - len, "%25s\t%u\n", "Mods failed on load", floads);
+
+	len += scnprintf(buf + len, size - len, "%25s\t%llu\n", "Total module size", total_size);
+	len += scnprintf(buf + len, size - len, "%25s\t%llu\n", "Total mod text size", text_size);
+
+	len += scnprintf(buf + len, size - len, "%25s\t%llu\n", "Failed kread bytes", ikread_bytes);
+
+	len += scnprintf(buf + len, size - len, "%25s\t%llu\n", "Failed decompress bytes",
+			 idecompress_bytes);
+
+	len += scnprintf(buf + len, size - len, "%25s\t%llu\n", "Failed becoming bytes", ibecoming_bytes);
+
+	len += scnprintf(buf + len, size - len, "%25s\t%llu\n", "Failed kmod bytes", imod_bytes);
+
+	len += scnprintf(buf + len, size - len, "%25s\t%llu\n", "Virtual mem wasted bytes", total_virtual_lost);
+
+	if (live_mod_count && total_size) {
+		len += scnprintf(buf + len, size - len, "%25s\t%llu\n", "Average mod size",
+				 DIV_ROUND_UP(total_size, live_mod_count));
+	}
+
+	if (live_mod_count && text_size) {
+		len += scnprintf(buf + len, size - len, "%25s\t%llu\n", "Average mod text size",
+				 DIV_ROUND_UP(text_size, live_mod_count));
+	}
+
+	/*
+	 * We use WARN_ON_ONCE() for the counters to ensure we always have parity
+	 * for keeping tabs on a type of failure with one type of byte counter.
+	 * The counters for imod_bytes does not increase for fkreads failures
+	 * for example, and so on.
+	 */
+
+	WARN_ON_ONCE(ikread_bytes && !fkreads);
+	if (fkreads && ikread_bytes) {
+		len += scnprintf(buf + len, size - len, "%25s\t%llu\n", "Avg fail kread bytes",
+				 DIV_ROUND_UP(ikread_bytes, fkreads));
+	}
+
+	WARN_ON_ONCE(ibecoming_bytes && !fbecoming);
+	if (fbecoming && ibecoming_bytes) {
+		len += scnprintf(buf + len, size - len, "%25s\t%llu\n", "Avg fail becoming bytes",
+				 DIV_ROUND_UP(ibecoming_bytes, fbecoming));
+	}
+
+	WARN_ON_ONCE(idecompress_bytes && !fdecompress);
+	if (fdecompress && idecompress_bytes) {
+		len += scnprintf(buf + len, size - len, "%25s\t%llu\n", "Avg fail decomp bytes",
+				 DIV_ROUND_UP(idecompress_bytes, fdecompress));
+	}
+
+	WARN_ON_ONCE(imod_bytes && !floads);
+	if (floads && imod_bytes) {
+		len += scnprintf(buf + len, size - len, "%25s\t%llu\n", "Average fail load bytes",
+				 DIV_ROUND_UP(imod_bytes, floads));
+	}
+
+	/* End of our debug preamble header. */
+
+	/* Catch when we've gone beyond our expected preamble */
+	WARN_ON_ONCE(len >= MAX_PREAMBLE);
+
+	if (list_empty(&dup_failed_modules))
+		goto out;
+
+	len += scnprintf(buf + len, size - len, "Duplicate failed modules:\n");
+	len += scnprintf(buf + len, size - len, "%25s\t%15s\t%25s\n",
+			 "Module-name", "How-many-times", "Reason");
+	mutex_lock(&module_mutex);
+
+
+	list_for_each_entry_rcu(mod_fail, &dup_failed_modules, list) {
+		if (WARN_ON_ONCE(++count_failed >= MAX_FAILED_MOD_PRINT))
+			goto out_unlock;
+		len += scnprintf(buf + len, size - len, "%25s\t%15llu\t%25s\n", mod_fail->name,
+				 atomic64_read(&mod_fail->count), mod_fail_to_str(mod_fail));
+	}
+out_unlock:
+	mutex_unlock(&module_mutex);
+out:
+	kfree(buf);
+        return simple_read_from_buffer(user_buf, count, ppos, buf, len);
+}
+#undef MAX_PREAMBLE
+#undef MAX_FAILED_MOD_PRINT
+#undef MAX_BYTES_PER_MOD
+
+static const struct file_operations fops_mod_stats = {
+	.read = read_file_mod_stats,
+	.open = simple_open,
+	.owner = THIS_MODULE,
+	.llseek = default_llseek,
+};
+
+#define mod_debug_add_ulong(name) debugfs_create_ulong(#name, 0400, mod_debugfs_root, (unsigned long *) &name.counter)
+#define mod_debug_add_atomic(name) debugfs_create_atomic_t(#name, 0400, mod_debugfs_root, &name)
+static int __init module_stats_init(void)
+{
+	mod_debug_add_ulong(total_mod_size);
+	mod_debug_add_ulong(total_text_size);
+	mod_debug_add_ulong(invalid_kread_bytes);
+	mod_debug_add_ulong(invalid_decompress_bytes);
+	mod_debug_add_ulong(invalid_becoming_bytes);
+	mod_debug_add_ulong(invalid_mod_bytes);
+
+	mod_debug_add_atomic(modcount);
+	mod_debug_add_atomic(failed_kreads);
+	mod_debug_add_atomic(failed_decompress);
+	mod_debug_add_atomic(failed_becoming);
+	mod_debug_add_atomic(failed_load_modules);
+
+	debugfs_create_file("stats", 0400, mod_debugfs_root, mod_debugfs_root, &fops_mod_stats);
+
+	return 0;
+}
+#undef mod_debug_add_ulong
+#undef mod_debug_add_atomic
+module_init(module_stats_init);
@@ -15,6 +15,7 @@
 #include "internal.h"

 static LIST_HEAD(unloaded_tainted_modules);
+extern struct dentry *mod_debugfs_root;

 int try_add_tainted_module(struct module *mod)
 {
@@ -120,12 +121,8 @@ static const struct file_operations unloaded_tainted_modules_fops = {

 static int __init unloaded_tainted_modules_init(void)
 {
-	struct dentry *dir;
-
-	dir = debugfs_create_dir("modules", NULL);
-	debugfs_create_file("unloaded_tainted", 0444, dir, NULL,
+	debugfs_create_file("unloaded_tainted", 0444, mod_debugfs_root, NULL,
 			    &unloaded_tainted_modules_fops);
-
 	return 0;
 }
 module_init(unloaded_tainted_modules_init);
@@ -0,0 +1 @@
+# CONFIG_MODULE_DEBUG is not set
@@ -0,0 +1 @@
+# CONFIG_MODULE_STATS is not set