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![Luis Chamberlain](/assets/img/avatar_default.png)
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>
129 lines
3.2 KiB
C
129 lines
3.2 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Module taint unload tracking support
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*
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* Copyright (C) 2022 Aaron Tomlin
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*/
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#include <linux/module.h>
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#include <linux/string.h>
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#include <linux/printk.h>
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#include <linux/slab.h>
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#include <linux/list.h>
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#include <linux/debugfs.h>
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#include <linux/rculist.h>
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#include "internal.h"
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static LIST_HEAD(unloaded_tainted_modules);
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extern struct dentry *mod_debugfs_root;
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int try_add_tainted_module(struct module *mod)
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{
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struct mod_unload_taint *mod_taint;
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module_assert_mutex_or_preempt();
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if (!mod->taints)
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goto out;
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list_for_each_entry_rcu(mod_taint, &unloaded_tainted_modules, list,
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lockdep_is_held(&module_mutex)) {
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if (!strcmp(mod_taint->name, mod->name) &&
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mod_taint->taints & mod->taints) {
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mod_taint->count++;
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goto out;
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}
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}
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mod_taint = kmalloc(sizeof(*mod_taint), GFP_KERNEL);
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if (unlikely(!mod_taint))
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return -ENOMEM;
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strscpy(mod_taint->name, mod->name, MODULE_NAME_LEN);
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mod_taint->taints = mod->taints;
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list_add_rcu(&mod_taint->list, &unloaded_tainted_modules);
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mod_taint->count = 1;
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out:
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return 0;
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}
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void print_unloaded_tainted_modules(void)
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{
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struct mod_unload_taint *mod_taint;
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char buf[MODULE_FLAGS_BUF_SIZE];
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if (!list_empty(&unloaded_tainted_modules)) {
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printk(KERN_DEFAULT "Unloaded tainted modules:");
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list_for_each_entry_rcu(mod_taint, &unloaded_tainted_modules,
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list) {
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size_t l;
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l = module_flags_taint(mod_taint->taints, buf);
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buf[l++] = '\0';
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pr_cont(" %s(%s):%llu", mod_taint->name, buf,
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mod_taint->count);
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}
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}
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}
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#ifdef CONFIG_DEBUG_FS
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static void *unloaded_tainted_modules_seq_start(struct seq_file *m, loff_t *pos)
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__acquires(rcu)
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{
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rcu_read_lock();
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return seq_list_start_rcu(&unloaded_tainted_modules, *pos);
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}
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static void *unloaded_tainted_modules_seq_next(struct seq_file *m, void *p, loff_t *pos)
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{
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return seq_list_next_rcu(p, &unloaded_tainted_modules, pos);
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}
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static void unloaded_tainted_modules_seq_stop(struct seq_file *m, void *p)
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__releases(rcu)
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{
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rcu_read_unlock();
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}
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static int unloaded_tainted_modules_seq_show(struct seq_file *m, void *p)
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{
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struct mod_unload_taint *mod_taint;
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char buf[MODULE_FLAGS_BUF_SIZE];
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size_t l;
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mod_taint = list_entry(p, struct mod_unload_taint, list);
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l = module_flags_taint(mod_taint->taints, buf);
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buf[l++] = '\0';
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seq_printf(m, "%s (%s) %llu", mod_taint->name, buf, mod_taint->count);
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seq_puts(m, "\n");
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return 0;
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}
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static const struct seq_operations unloaded_tainted_modules_seq_ops = {
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.start = unloaded_tainted_modules_seq_start,
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.next = unloaded_tainted_modules_seq_next,
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.stop = unloaded_tainted_modules_seq_stop,
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.show = unloaded_tainted_modules_seq_show,
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};
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static int unloaded_tainted_modules_open(struct inode *inode, struct file *file)
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{
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return seq_open(file, &unloaded_tainted_modules_seq_ops);
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}
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static const struct file_operations unloaded_tainted_modules_fops = {
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.open = unloaded_tainted_modules_open,
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.read = seq_read,
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.llseek = seq_lseek,
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.release = seq_release,
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};
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static int __init unloaded_tainted_modules_init(void)
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{
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debugfs_create_file("unloaded_tainted", 0444, mod_debugfs_root, NULL,
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&unloaded_tainted_modules_fops);
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return 0;
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}
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module_init(unloaded_tainted_modules_init);
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#endif /* CONFIG_DEBUG_FS */
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