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 its not at all clear to me the required locking is observed, esp. on exported functions. Cc: Rusty Russell Acked-by: "Paul E. McKenney" Signed-off-by: Peter Zijlstra (Intel) --- include/linux/module.h | 12 ++++++++++-- kernel/module.c | 42 ++++++++++++++++++++++++++++++++++-------- lib/bug.c | 7 +++++-- 3 files changed, 49 insertions(+), 12 deletions(-) --- a/include/linux/module.h +++ b/include/linux/module.h @@ -415,14 +415,22 @@ struct symsearch { bool unused; }; -/* Search for an exported symbol by name. */ +/* + * Search for an exported symbol by name. + * + * Must be called with module_mutex held or preemption disabled. + */ const struct kernel_symbol *find_symbol(const char *name, struct module **owner, const unsigned long **crc, bool gplok, bool warn); -/* Walk the exported symbol table */ +/* + * Walk the exported symbol table + * + * Must be called with module_mutex held or preemption disabled. + */ bool each_symbol_section(bool (*fn)(const struct symsearch *arr, struct module *owner, void *data), void *data); --- a/kernel/module.c +++ b/kernel/module.c @@ -106,6 +106,24 @@ static LIST_HEAD(modules); struct list_head *kdb_modules = &modules; /* kdb needs the list of modules */ #endif /* CONFIG_KGDB_KDB */ +static void module_assert_mutex(void) +{ + lockdep_assert_held(&module_mutex); +} + +static void module_assert_mutex_or_preempt(void) +{ +#ifdef CONFIG_LOCKDEP + int rcu_held = rcu_read_lock_sched_held(); + int mutex_held = 1; + + if (debug_locks) + mutex_held = lockdep_is_held(&module_mutex); + + WARN_ON(!rcu_held && !mutex_held); +#endif +} + #ifdef CONFIG_MODULE_SIG #ifdef CONFIG_MODULE_SIG_FORCE static bool sig_enforce = true; @@ -319,6 +337,8 @@ bool each_symbol_section(bool (*fn)(cons #endif }; + module_assert_mutex_or_preempt(); + if (each_symbol_in_section(arr, ARRAY_SIZE(arr), NULL, fn, data)) return true; @@ -458,6 +478,8 @@ static struct module *find_module_all(co { struct module *mod; + module_assert_mutex(); + list_for_each_entry(mod, &modules, list) { if (!even_unformed && mod->state == MODULE_STATE_UNFORMED) continue; @@ -1856,8 +1878,8 @@ static void free_module(struct module *m list_del_rcu(&mod->list); /* Remove this module from bug list, this uses list_del_rcu */ module_bug_cleanup(mod); - /* Wait for RCU synchronizing before releasing mod->list and buglist. */ - synchronize_rcu(); + /* Wait for RCU-sched synchronizing before releasing mod->list and buglist. */ + synchronize_sched(); mutex_unlock(&module_mutex); /* This may be NULL, but that's OK */ @@ -3106,11 +3128,11 @@ static noinline int do_init_module(struc mod->init_text_size = 0; /* * We want to free module_init, but be aware that kallsyms may be - * walking this with preempt disabled. In all the failure paths, - * we call synchronize_rcu/synchronize_sched, but we don't want - * to slow down the success path, so use actual RCU here. + * walking this with preempt disabled. In all the failure paths, we + * call synchronize_sched, but we don't want to slow down the success + * path, so use actual RCU here. */ - call_rcu(&freeinit->rcu, do_free_init); + call_rcu_sched(&freeinit->rcu, do_free_init); mutex_unlock(&module_mutex); wake_up_all(&module_wq); @@ -3368,8 +3390,8 @@ static int load_module(struct load_info /* Unlink carefully: kallsyms could be walking list. */ list_del_rcu(&mod->list); wake_up_all(&module_wq); - /* Wait for RCU synchronizing before releasing mod->list. */ - synchronize_rcu(); + /* Wait for RCU-sched synchronizing before releasing mod->list. */ + synchronize_sched(); mutex_unlock(&module_mutex); free_module: /* Free lock-classes; relies on the preceding sync_rcu() */ @@ -3636,6 +3658,8 @@ int module_kallsyms_on_each_symbol(int ( unsigned int i; int ret; + module_assert_mutex(); + list_for_each_entry(mod, &modules, list) { if (mod->state == MODULE_STATE_UNFORMED) continue; @@ -3810,6 +3834,8 @@ struct module *__module_address(unsigned if (addr < module_addr_min || addr > module_addr_max) return NULL; + module_assert_mutex_or_preempt(); + list_for_each_entry_rcu(mod, &modules, list) { if (mod->state == MODULE_STATE_UNFORMED) continue; --- a/lib/bug.c +++ b/lib/bug.c @@ -66,7 +66,7 @@ static const struct bug_entry *module_fi struct module *mod; const struct bug_entry *bug = NULL; - rcu_read_lock(); + rcu_read_lock_sched(); list_for_each_entry_rcu(mod, &module_bug_list, bug_list) { unsigned i; @@ -77,7 +77,7 @@ static const struct bug_entry *module_fi } bug = NULL; out: - rcu_read_unlock(); + rcu_read_unlock_sched(); return bug; } @@ -88,6 +88,8 @@ void module_bug_finalize(const Elf_Ehdr char *secstrings; unsigned int i; + lockdep_assert_held(&module_mutex); + mod->bug_table = NULL; mod->num_bugs = 0; @@ -113,6 +115,7 @@ void module_bug_finalize(const Elf_Ehdr void module_bug_cleanup(struct module *mod) { + lockdep_assert_held(&module_mutex); list_del_rcu(&mod->bug_list); } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/