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Diffstat (limited to 'kernel/module/stats.c')
| -rw-r--r-- | kernel/module/stats.c | 430 |
1 files changed, 430 insertions, 0 deletions
diff --git a/kernel/module/stats.c b/kernel/module/stats.c new file mode 100644 index 000000000000..3d45744b3920 --- /dev/null +++ b/kernel/module/stats.c @@ -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); |