[ 36/46] module: put modules in list much earlier.

Greg Kroah-Hartman
2013-01-24T21:31:13Z

From: Rusty Russell <rusty@rustcorp.com.au>

commit 1fb9341ac34825aa40354e74d9a2c69df7d2c304 upstream.

Prarit's excellent bug report:
> In recent Fedora releases (F17 & F18) some users have reported seeing
> messages similar to
>
> [ 15.478160] kvm: Could not allocate 304 bytes percpu data
> [ 15.478174] PERCPU: allocation failed, size=304 align=32, alloc from
> reserved chunk failed
>
> during system boot. In some cases, users have also reported seeing this
> message along with a failed load of other modules.
>
> What is happening is systemd is loading an instance of the kvm module for
> each cpu found (see commit e9bda3b). When the module load occurs the kernel
> currently allocates the modules percpu data area prior to checking to see
> if the module is already loaded or is in the process of being loaded. If
> the module is already loaded, or finishes load, the module loading code
> releases the current instance's module's percpu data.

Now we have a new state MODULE_STATE_UNFORMED, we can insert the
module into the list (and thus guarantee its uniqueness) before we
allocate the per-cpu region.

Reported-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Tested-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/module.c | 90 ++++++++++++++++++++++++++++++--------------------------
lib/bug.c | 1
2 files changed, 50 insertions(+), 41 deletions(-)

--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2958,7 +2958,7 @@ static bool finished_loading(const char
bool ret;

mutex_lock(&module_mutex);
- mod = find_module(name);
+ mod = find_module_all(name, true);
ret = !mod || mod->state == MODULE_STATE_LIVE
|| mod->state == MODULE_STATE_GOING;
mutex_unlock(&module_mutex);
@@ -2991,6 +2991,32 @@ static struct module *load_module(void _
goto free_copy;
}

+ /*
+ * We try to place it in the list now to make sure it's unique
+ * before we dedicate too many resources. In particular,
+ * temporary percpu memory exhaustion.
+ */
+ mod->state = MODULE_STATE_UNFORMED;
+again:
+ mutex_lock(&module_mutex);
+ if ((old = find_module_all(mod->name, true)) != NULL) {
+ if (old->state == MODULE_STATE_COMING
+ || old->state == MODULE_STATE_UNFORMED) {
+ /* Wait in case it fails to load. */
+ mutex_unlock(&module_mutex);
+ err = wait_event_interruptible(module_wq,
+ finished_loading(mod->name));
+ if (err)
+ goto free_module;
+ goto again;
+ }
+ err = -EEXIST;
+ mutex_unlock(&module_mutex);
+ goto free_module;
+ }
+ list_add_rcu(&mod->list, &modules);
+ mutex_unlock(&module_mutex);
+
#ifdef CONFIG_MODULE_SIG
mod->sig_ok = info.sig_ok;
if (!mod->sig_ok)
@@ -3000,7 +3026,7 @@ static struct module *load_module(void _
/* Now module is in final location, initialize linked lists, etc. */
err = module_unload_init(mod);
if (err)
- goto free_module;
+ goto unlink_mod;

/* Now we've got everything in the final locations, we can
* find optional sections. */
@@ -3035,54 +3061,33 @@ static struct module *load_module(void _
goto free_arch_cleanup;
}

- /* Mark state as coming so strong_try_module_get() ignores us. */
- mod->state = MODULE_STATE_COMING;
-
- /* Now sew it into the lists so we can get lockdep and oops
- * info during argument parsing. No one should access us, since
- * strong_try_module_get() will fail.
- * lockdep/oops can run asynchronous, so use the RCU list insertion
- * function to insert in a way safe to concurrent readers.
- * The mutex protects against concurrent writers.
- */
-again:
- mutex_lock(&module_mutex);
- if ((old = find_module(mod->name)) != NULL) {
- if (old->state == MODULE_STATE_COMING) {
- /* Wait in case it fails to load. */
- mutex_unlock(&module_mutex);
- err = wait_event_interruptible(module_wq,
- finished_loading(mod->name));
- if (err)
- goto free_arch_cleanup;
- goto again;
- }
- err = -EEXIST;
- goto unlock;
- }
-
- /* This has to be done once we're sure module name is unique. */
dynamic_debug_setup(info.debug, info.num_debug);

- /* Find duplicate symbols */
+ mutex_lock(&module_mutex);
+ /* Find duplicate symbols (must be called under lock). */
err = verify_export_symbols(mod);
if (err < 0)
- goto ddebug;
+ goto ddebug_cleanup;

+ /* This relies on module_mutex for list integrity. */
module_bug_finalize(info.hdr, info.sechdrs, mod);
- list_add_rcu(&mod->list, &modules);
+
+ /* Mark state as coming so strong_try_module_get() ignores us,
+ * but kallsyms etc. can see us. */
+ mod->state = MODULE_STATE_COMING;
+
mutex_unlock(&module_mutex);

/* Module is ready to execute: parsing args may do that. */
err = parse_args(mod->name, mod->args, mod->kp, mod->num_kp,
-32768, 32767, &ddebug_dyndbg_module_param_cb);
if (err < 0)
- goto unlink;
+ goto bug_cleanup;

/* Link in to syfs. */
err = mod_sysfs_setup(mod, &info, mod->kp, mod->num_kp);
if (err < 0)
- goto unlink;
+ goto bug_cleanup;

/* Get rid of temporary copy. */
free_copy(&info);
@@ -3091,16 +3096,13 @@ again:
trace_module_load(mod);
return mod;

- unlink:
+ bug_cleanup:
+ /* module_bug_cleanup needs module_mutex protection */
mutex_lock(&module_mutex);
- /* Unlink carefully: kallsyms could be walking list. */
- list_del_rcu(&mod->list);
module_bug_cleanup(mod);
- wake_up_all(&module_wq);
- ddebug:
- dynamic_debug_remove(info.debug);
- unlock:
mutex_unlock(&module_mutex);
+ ddebug_cleanup:
+ dynamic_debug_remove(info.debug);
synchronize_sched();
kfree(mod->args);
free_arch_cleanup:
@@ -3109,6 +3111,12 @@ again:
free_modinfo(mod);
free_unload:
module_unload_free(mod);
+ unlink_mod:
+ mutex_lock(&module_mutex);
+ /* Unlink carefully: kallsyms could be walking list. */
+ list_del_rcu(&mod->list);
+ wake_up_all(&module_wq);
+ mutex_unlock(&module_mutex);
free_module:
module_deallocate(mod, &info);
free_copy:
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -55,6 +55,7 @@ static inline unsigned long bug_addr(con
}

#ifdef CONFIG_MODULES
+/* Updates are protected by module mutex */
static LIST_HEAD(module_bug_list);

static const struct bug_entry *module_find_bug(unsigned long bugaddr)