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-rw-r--r--kernel/module/stats.c430
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diff --git a/kernel/module/stats.c b/kernel/module/stats.c
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+// 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 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;
+ 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:
+ 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);