// SPDX-License-Identifier: GPL-2.0-or-later/* * Debugging module statistics. * * Copyright (C) 2023 Luis Chamberlain <mcgrof@kernel.org> */ #include <linux/module.h>#include <uapi/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(). *	- 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 can 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(). The check for module_patient_check_exists() *     at the end of early_mod_check() prevents 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_bytes);#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 64static 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;	int ret;	u32 live_mod_count, fkreads, fdecompress, fbecoming, floads;	unsigned long 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 = atomic_long_read(&total_mod_size);	text_size = atomic_long_read(&total_text_size);	ikread_bytes = atomic_long_read(&invalid_kread_bytes);	idecompress_bytes = atomic_long_read(&invalid_decompress_bytes);	ibecoming_bytes = atomic_long_read(&invalid_becoming_bytes);	imod_bytes = atomic_long_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, size, "%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%lu\n", "Total module size", total_size);	len += scnprintf(buf + len, size - len, "%25s\t%lu\n", "Total mod text size", text_size); 	len += scnprintf(buf + len, size - len, "%25s\t%lu\n", "Failed kread bytes", ikread_bytes); 	len += scnprintf(buf + len, size - len, "%25s\t%lu\n", "Failed decompress bytes",			 idecompress_bytes); 	len += scnprintf(buf + len, size - len, "%25s\t%lu\n", "Failed becoming bytes", ibecoming_bytes); 	len += scnprintf(buf + len, size - len, "%25s\t%lu\n", "Failed kmod bytes", imod_bytes); 	len += scnprintf(buf + len, size - len, "%25s\t%lu\n", "Virtual mem wasted bytes", total_virtual_lost); 	if (live_mod_count && total_size) {		len += scnprintf(buf + len, size - len, "%25s\t%lu\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%lu\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%lu\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%lu\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%lu\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%lu\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%15lu\t%25s\n", mod_fail->name,				 atomic_long_read(&mod_fail->count), mod_fail_to_str(mod_fail));	}out_unlock:	mutex_unlock(&module_mutex);out:	ret = simple_read_from_buffer(user_buf, count, ppos, buf, len);	kfree(buf);	return ret;}#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_atomicmodule_init(module_stats_init);