Commit 0be964be authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Rusty Russell

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: default avatar"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent bed831f9
......@@ -421,14 +421,22 @@ 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);
......
......@@ -105,6 +105,22 @@ 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
if (unlikely(!debug_locks))
return;
WARN_ON(!rcu_read_lock_sched_held() &&
!lockdep_is_held(&module_mutex));
#endif
}
#ifdef CONFIG_MODULE_SIG
#ifdef CONFIG_MODULE_SIG_FORCE
static bool sig_enforce = true;
......@@ -318,6 +334,8 @@ bool each_symbol_section(bool (*fn)(const struct symsearch *arr,
#endif
};
module_assert_mutex_or_preempt();
if (each_symbol_in_section(arr, ARRAY_SIZE(arr), NULL, fn, data))
return true;
......@@ -457,6 +475,8 @@ static struct module *find_module_all(const char *name, size_t len,
{
struct module *mod;
module_assert_mutex();
list_for_each_entry(mod, &modules, list) {
if (!even_unformed && mod->state == MODULE_STATE_UNFORMED)
continue;
......@@ -1860,8 +1880,8 @@ static void free_module(struct module *mod)
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 */
......@@ -3133,11 +3153,11 @@ static noinline int do_init_module(struct module *mod)
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);
......@@ -3395,8 +3415,8 @@ static int load_module(struct load_info *info, const char __user *uargs,
/* 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() */
......@@ -3663,6 +3683,8 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,
unsigned int i;
int ret;
module_assert_mutex();
list_for_each_entry(mod, &modules, list) {
if (mod->state == MODULE_STATE_UNFORMED)
continue;
......@@ -3837,6 +3859,8 @@ struct module *__module_address(unsigned long addr)
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;
......
......@@ -66,7 +66,7 @@ static const struct bug_entry *module_find_bug(unsigned long bugaddr)
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_find_bug(unsigned long bugaddr)
}
bug = NULL;
out:
rcu_read_unlock();
rcu_read_unlock_sched();
return bug;
}
......@@ -88,6 +88,8 @@ void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
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 *hdr, const Elf_Shdr *sechdrs,
void module_bug_cleanup(struct module *mod)
{
lockdep_assert_held(&module_mutex);
list_del_rcu(&mod->bug_list);
}
......
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