// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Debugging module statistics.
*
* Copyright (C) 2023 Luis Chamberlain <[email protected]>
*/
#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
* 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;
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_atomic
module_init(module_stats_init);
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