module: Sanitize RCU usage and locking
Currently the RCU usage in module is an inconsistent mess of RCU and RCU-sched, this is broken for CONFIG_PREEMPT where synchronize_rcu() does not imply synchronize_sched(). Most usage sites use preempt_{dis,en}able() which is RCU-sched, but (most of) the modification sites use synchronize_rcu(). With the exception of the module bug list, which actually uses RCU. Convert everything over to RCU-sched. Furthermore add lockdep asserts to all sites, because it's not at all clear to me the required locking is observed, esp. on exported functions. Cc: Rusty Russell <rusty@rustcorp.com.au> Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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@ -421,14 +421,22 @@ struct symsearch {
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bool unused;
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};
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/* Search for an exported symbol by name. */
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/*
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* Search for an exported symbol by name.
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*
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* Must be called with module_mutex held or preemption disabled.
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*/
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const struct kernel_symbol *find_symbol(const char *name,
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struct module **owner,
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const unsigned long **crc,
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bool gplok,
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bool warn);
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/* Walk the exported symbol table */
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/*
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* Walk the exported symbol table
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*
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* Must be called with module_mutex held or preemption disabled.
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*/
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bool each_symbol_section(bool (*fn)(const struct symsearch *arr,
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struct module *owner,
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void *data), void *data);
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@ -105,6 +105,22 @@ static LIST_HEAD(modules);
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struct list_head *kdb_modules = &modules; /* kdb needs the list of modules */
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#endif /* CONFIG_KGDB_KDB */
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static void module_assert_mutex(void)
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{
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lockdep_assert_held(&module_mutex);
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}
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static void module_assert_mutex_or_preempt(void)
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{
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#ifdef CONFIG_LOCKDEP
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if (unlikely(!debug_locks))
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return;
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WARN_ON(!rcu_read_lock_sched_held() &&
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!lockdep_is_held(&module_mutex));
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#endif
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}
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#ifdef CONFIG_MODULE_SIG
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#ifdef CONFIG_MODULE_SIG_FORCE
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static bool sig_enforce = true;
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@ -318,6 +334,8 @@ bool each_symbol_section(bool (*fn)(const struct symsearch *arr,
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#endif
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};
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module_assert_mutex_or_preempt();
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if (each_symbol_in_section(arr, ARRAY_SIZE(arr), NULL, fn, data))
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return true;
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@ -457,6 +475,8 @@ static struct module *find_module_all(const char *name, size_t len,
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{
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struct module *mod;
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module_assert_mutex();
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list_for_each_entry(mod, &modules, list) {
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if (!even_unformed && mod->state == MODULE_STATE_UNFORMED)
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continue;
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@ -1860,8 +1880,8 @@ static void free_module(struct module *mod)
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list_del_rcu(&mod->list);
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/* Remove this module from bug list, this uses list_del_rcu */
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module_bug_cleanup(mod);
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/* Wait for RCU synchronizing before releasing mod->list and buglist. */
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synchronize_rcu();
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/* Wait for RCU-sched synchronizing before releasing mod->list and buglist. */
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synchronize_sched();
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mutex_unlock(&module_mutex);
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/* This may be NULL, but that's OK */
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@ -3133,11 +3153,11 @@ static noinline int do_init_module(struct module *mod)
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mod->init_text_size = 0;
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/*
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* We want to free module_init, but be aware that kallsyms may be
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* walking this with preempt disabled. In all the failure paths,
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* we call synchronize_rcu/synchronize_sched, but we don't want
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* to slow down the success path, so use actual RCU here.
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* walking this with preempt disabled. In all the failure paths, we
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* call synchronize_sched(), but we don't want to slow down the success
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* path, so use actual RCU here.
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*/
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call_rcu(&freeinit->rcu, do_free_init);
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call_rcu_sched(&freeinit->rcu, do_free_init);
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mutex_unlock(&module_mutex);
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wake_up_all(&module_wq);
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@ -3395,8 +3415,8 @@ static int load_module(struct load_info *info, const char __user *uargs,
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/* Unlink carefully: kallsyms could be walking list. */
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list_del_rcu(&mod->list);
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wake_up_all(&module_wq);
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/* Wait for RCU synchronizing before releasing mod->list. */
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synchronize_rcu();
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/* Wait for RCU-sched synchronizing before releasing mod->list. */
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synchronize_sched();
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mutex_unlock(&module_mutex);
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free_module:
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/* Free lock-classes; relies on the preceding sync_rcu() */
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@ -3663,6 +3683,8 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,
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unsigned int i;
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int ret;
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module_assert_mutex();
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list_for_each_entry(mod, &modules, list) {
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if (mod->state == MODULE_STATE_UNFORMED)
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continue;
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@ -3837,6 +3859,8 @@ struct module *__module_address(unsigned long addr)
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if (addr < module_addr_min || addr > module_addr_max)
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return NULL;
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module_assert_mutex_or_preempt();
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list_for_each_entry_rcu(mod, &modules, list) {
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if (mod->state == MODULE_STATE_UNFORMED)
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continue;
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@ -66,7 +66,7 @@ static const struct bug_entry *module_find_bug(unsigned long bugaddr)
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struct module *mod;
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const struct bug_entry *bug = NULL;
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rcu_read_lock();
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rcu_read_lock_sched();
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list_for_each_entry_rcu(mod, &module_bug_list, bug_list) {
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unsigned i;
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@ -77,7 +77,7 @@ static const struct bug_entry *module_find_bug(unsigned long bugaddr)
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}
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bug = NULL;
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out:
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rcu_read_unlock();
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rcu_read_unlock_sched();
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return bug;
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}
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@ -88,6 +88,8 @@ void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
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char *secstrings;
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unsigned int i;
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lockdep_assert_held(&module_mutex);
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mod->bug_table = NULL;
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mod->num_bugs = 0;
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@ -113,6 +115,7 @@ void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
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void module_bug_cleanup(struct module *mod)
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{
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lockdep_assert_held(&module_mutex);
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list_del_rcu(&mod->bug_list);
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}
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