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The RCU usage in module was introduced in commitd72b37513c("Remove stop_machine during module load v2") and it claimed not to be RCU but similar. Then there was another improvement in commite91defa26c("module: don't use stop_machine on module load"). It become a mix of RCU and RCU-sched and was eventually fixed0be964be0d("module: Sanitize RCU usage and locking"). Later RCU & RCU-sched was merged in commitcb2f55369d("modules: Replace synchronize_sched() and call_rcu_sched()") so that was aligned. Looking at it today, there is still leftovers. The preempt_disable() was used instead rcu_read_lock_sched(). The RCU & RCU-sched merge was not complete as there is still rcu_dereference_sched() for module::kallsyms. The RCU-list modules and unloaded_tainted_modules are always accessed under RCU protection or the module_mutex. The modules list iteration can always happen safely because the module will not disappear. Once the module is removed (free_module()) then after removing the module from the list, there is a synchronize_rcu() which waits until every RCU reader left the section. That means iterating over the list within a RCU-read section is enough, there is no need to disable preemption. module::kallsyms is first assigned in add_kallsyms() before the module is added to the list. At this point, it points to init data. This pointer is later updated and before the init code is removed there is also synchronize_rcu() in do_free_init(). That means A RCU read lock is enough for protection and rcu_dereference() can be safely used. Convert module code and its users step by step. Update comments and convert print_modules() to use RCU. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20250108090457.512198-3-bigeasy@linutronix.de Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
112 lines
2.6 KiB
C
112 lines
2.6 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Modules tree lookup
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*
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* Copyright (C) 2015 Peter Zijlstra
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* Copyright (C) 2015 Rusty Russell
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*/
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#include <linux/module.h>
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#include <linux/rbtree_latch.h>
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#include "internal.h"
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/*
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* Use a latched RB-tree for __module_address(); this allows us to use
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* RCU lookups of the address from any context.
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*
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* This is conditional on PERF_EVENTS || TRACING || CFI_CLANG because those can
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* really hit __module_address() hard by doing a lot of stack unwinding;
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* potentially from NMI context.
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*/
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static __always_inline unsigned long __mod_tree_val(struct latch_tree_node *n)
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{
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struct module_memory *mod_mem = container_of(n, struct module_memory, mtn.node);
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return (unsigned long)mod_mem->base;
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}
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static __always_inline unsigned long __mod_tree_size(struct latch_tree_node *n)
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{
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struct module_memory *mod_mem = container_of(n, struct module_memory, mtn.node);
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return (unsigned long)mod_mem->size;
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}
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static __always_inline bool
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mod_tree_less(struct latch_tree_node *a, struct latch_tree_node *b)
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{
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return __mod_tree_val(a) < __mod_tree_val(b);
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}
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static __always_inline int
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mod_tree_comp(void *key, struct latch_tree_node *n)
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{
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unsigned long val = (unsigned long)key;
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unsigned long start, end;
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start = __mod_tree_val(n);
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if (val < start)
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return -1;
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end = start + __mod_tree_size(n);
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if (val >= end)
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return 1;
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return 0;
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}
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static const struct latch_tree_ops mod_tree_ops = {
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.less = mod_tree_less,
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.comp = mod_tree_comp,
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};
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static noinline void __mod_tree_insert(struct mod_tree_node *node, struct mod_tree_root *tree)
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{
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latch_tree_insert(&node->node, &tree->root, &mod_tree_ops);
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}
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static void __mod_tree_remove(struct mod_tree_node *node, struct mod_tree_root *tree)
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{
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latch_tree_erase(&node->node, &tree->root, &mod_tree_ops);
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}
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/*
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* These modifications: insert, remove_init and remove; are serialized by the
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* module_mutex.
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*/
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void mod_tree_insert(struct module *mod)
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{
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for_each_mod_mem_type(type) {
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mod->mem[type].mtn.mod = mod;
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if (mod->mem[type].size)
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__mod_tree_insert(&mod->mem[type].mtn, &mod_tree);
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}
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}
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void mod_tree_remove_init(struct module *mod)
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{
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for_class_mod_mem_type(type, init) {
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if (mod->mem[type].size)
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__mod_tree_remove(&mod->mem[type].mtn, &mod_tree);
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}
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}
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void mod_tree_remove(struct module *mod)
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{
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for_each_mod_mem_type(type) {
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if (mod->mem[type].size)
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__mod_tree_remove(&mod->mem[type].mtn, &mod_tree);
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}
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}
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struct module *mod_find(unsigned long addr, struct mod_tree_root *tree)
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{
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struct latch_tree_node *ltn;
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ltn = latch_tree_find((void *)addr, &tree->root, &mod_tree_ops);
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if (!ltn)
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return NULL;
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return container_of(ltn, struct mod_tree_node, node)->mod;
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}
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