module: make locking more fine-grained.
Kay Sievers <kay.sievers@vrfy.org> reports that we still have some
contention over module loading which is slowing boot.
Linus also disliked a previous "drop lock and regrab" patch to fix the
bne2 "gave up waiting for init of module libcrc32c" message.
This is more ambitious: we only grab the lock where we need it.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Brandon Philips <brandon@ifup.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/module.c b/kernel/module.c
index 808aa18..d293c21 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -72,7 +72,11 @@
/* If this is set, the section belongs in the init part of the module */
#define INIT_OFFSET_MASK (1UL << (BITS_PER_LONG-1))
-/* List of modules, protected by module_mutex or preempt_disable
+/*
+ * Mutex protects:
+ * 1) List of modules (also safely readable with preempt_disable),
+ * 2) module_use links,
+ * 3) module_addr_min/module_addr_max.
* (delete uses stop_machine/add uses RCU list operations). */
DEFINE_MUTEX(module_mutex);
EXPORT_SYMBOL_GPL(module_mutex);
@@ -90,7 +94,8 @@
static BLOCKING_NOTIFIER_HEAD(module_notify_list);
-/* Bounds of module allocation, for speeding __module_address */
+/* Bounds of module allocation, for speeding __module_address.
+ * Protected by module_mutex. */
static unsigned long module_addr_min = -1UL, module_addr_max = 0;
int register_module_notifier(struct notifier_block * nb)
@@ -329,7 +334,7 @@
}
/* Find a symbol and return it, along with, (optional) crc and
- * (optional) module which owns it */
+ * (optional) module which owns it. Needs preempt disabled or module_mutex. */
const struct kernel_symbol *find_symbol(const char *name,
struct module **owner,
const unsigned long **crc,
@@ -576,7 +581,7 @@
return 0;
}
-/* Module a uses b */
+/* Module a uses b: caller needs module_mutex() */
int use_module(struct module *a, struct module *b)
{
int err;
@@ -610,6 +615,7 @@
{
struct module_use *use, *tmp;
+ mutex_lock(&module_mutex);
list_for_each_entry_safe(use, tmp, &mod->target_list, target_list) {
struct module *i = use->target;
DEBUGP("%s unusing %s\n", mod->name, i->name);
@@ -618,6 +624,7 @@
list_del(&use->target_list);
kfree(use);
}
+ mutex_unlock(&module_mutex);
}
#ifdef CONFIG_MODULE_FORCE_UNLOAD
@@ -784,13 +791,14 @@
blocking_notifier_call_chain(&module_notify_list,
MODULE_STATE_GOING, mod);
async_synchronize_full();
- mutex_lock(&module_mutex);
+
/* Store the name of the last unloaded module for diagnostic purposes */
strlcpy(last_unloaded_module, mod->name, sizeof(last_unloaded_module));
ddebug_remove_module(mod->name);
- free_module(mod);
- out:
+ free_module(mod);
+ return 0;
+out:
mutex_unlock(&module_mutex);
return ret;
}
@@ -1006,6 +1014,8 @@
{
const unsigned long *crc;
+ /* Since this should be found in kernel (which can't be removed),
+ * no locking is necessary. */
if (!find_symbol(MODULE_SYMBOL_PREFIX "module_layout", NULL,
&crc, true, false))
BUG();
@@ -1048,8 +1058,7 @@
}
#endif /* CONFIG_MODVERSIONS */
-/* Resolve a symbol for this module. I.e. if we find one, record usage.
- Must be holding module_mutex. */
+/* Resolve a symbol for this module. I.e. if we find one, record usage. */
static const struct kernel_symbol *resolve_symbol(Elf_Shdr *sechdrs,
unsigned int versindex,
const char *name,
@@ -1059,6 +1068,7 @@
const struct kernel_symbol *sym;
const unsigned long *crc;
+ mutex_lock(&module_mutex);
sym = find_symbol(name, &owner, &crc,
!(mod->taints & (1 << TAINT_PROPRIETARY_MODULE)), true);
/* use_module can fail due to OOM,
@@ -1068,6 +1078,7 @@
|| !use_module(mod, owner))
sym = NULL;
}
+ mutex_unlock(&module_mutex);
return sym;
}
@@ -1306,10 +1317,12 @@
struct module_use *use;
int nowarn;
+ mutex_lock(&module_mutex);
list_for_each_entry(use, &mod->target_list, target_list) {
nowarn = sysfs_create_link(use->target->holders_dir,
&mod->mkobj.kobj, mod->name);
}
+ mutex_unlock(&module_mutex);
#endif
}
@@ -1318,8 +1331,10 @@
#ifdef CONFIG_MODULE_UNLOAD
struct module_use *use;
+ mutex_lock(&module_mutex);
list_for_each_entry(use, &mod->target_list, target_list)
sysfs_remove_link(use->target->holders_dir, mod->name);
+ mutex_unlock(&module_mutex);
#endif
}
@@ -1497,13 +1512,15 @@
return 0;
}
-/* Free a module, remove from lists, etc (must hold module_mutex). */
+/* Free a module, remove from lists, etc. */
static void free_module(struct module *mod)
{
trace_module_free(mod);
/* Delete from various lists */
+ mutex_lock(&module_mutex);
stop_machine(__unlink_module, mod, NULL);
+ mutex_unlock(&module_mutex);
remove_notes_attrs(mod);
remove_sect_attrs(mod);
mod_kobject_remove(mod);
@@ -1575,7 +1592,14 @@
for (i = 0; i < ARRAY_SIZE(arr); i++) {
for (s = arr[i].sym; s < arr[i].sym + arr[i].num; s++) {
- if (find_symbol(s->name, &owner, NULL, true, false)) {
+ const struct kernel_symbol *sym;
+
+ /* Stopping preemption makes find_symbol safe. */
+ preempt_disable();
+ sym = find_symbol(s->name, &owner, NULL, true, false);
+ preempt_enable();
+
+ if (sym) {
printk(KERN_ERR
"%s: exports duplicate symbol %s"
" (owned by %s)\n",
@@ -2021,11 +2045,13 @@
void *ret = module_alloc(size);
if (ret) {
+ mutex_lock(&module_mutex);
/* Update module bounds. */
if ((unsigned long)ret < module_addr_min)
module_addr_min = (unsigned long)ret;
if ((unsigned long)ret + size > module_addr_max)
module_addr_max = (unsigned long)ret + size;
+ mutex_unlock(&module_mutex);
}
return ret;
}
@@ -2482,7 +2508,9 @@
* function to insert in a way safe to concurrent readers.
* The mutex protects against concurrent writers.
*/
+ mutex_lock(&module_mutex);
list_add_rcu(&mod->list, &modules);
+ mutex_unlock(&module_mutex);
err = parse_args(mod->name, mod->args, mod->kp, mod->num_kp, NULL);
if (err < 0)
@@ -2504,8 +2532,10 @@
return mod;
unlink:
+ mutex_lock(&module_mutex);
/* Unlink carefully: kallsyms could be walking list. */
list_del_rcu(&mod->list);
+ mutex_unlock(&module_mutex);
synchronize_sched();
module_arch_cleanup(mod);
cleanup:
@@ -2556,19 +2586,10 @@
if (!capable(CAP_SYS_MODULE) || modules_disabled)
return -EPERM;
- /* Only one module load at a time, please */
- if (mutex_lock_interruptible(&module_mutex) != 0)
- return -EINTR;
-
/* Do all the hard work */
mod = load_module(umod, len, uargs);
- if (IS_ERR(mod)) {
- mutex_unlock(&module_mutex);
+ if (IS_ERR(mod))
return PTR_ERR(mod);
- }
-
- /* Drop lock so they can recurse */
- mutex_unlock(&module_mutex);
blocking_notifier_call_chain(&module_notify_list,
MODULE_STATE_COMING, mod);
@@ -2585,9 +2606,7 @@
module_put(mod);
blocking_notifier_call_chain(&module_notify_list,
MODULE_STATE_GOING, mod);
- mutex_lock(&module_mutex);
free_module(mod);
- mutex_unlock(&module_mutex);
wake_up(&module_wq);
return ret;
}