[PATCH v2 2/5] module: Unlink module with RCU synchronizing instead of stop_machine

Masami Hiramatsu
2014-10-23T11:30:41Z

Unlink module from module list with RCU synchronizing instead
of using stop_machine(). Since module list is already protected
by rcu, we don't need stop_machine() anymore.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
---
kernel/module.c | 18 +++++-------------
1 file changed, 5 insertions(+), 13 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 331b03f..bed608b 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1697,18 +1697,6 @@ static void mod_sysfs_teardown(struct module *mod)
mod_sysfs_fini(mod);
}

-/*
- * unlink the module with the whole machine is stopped with interrupts off
- * - this defends against kallsyms not taking locks
- */
-static int __unlink_module(void *_mod)
-{
- struct module *mod = _mod;
- list_del(&mod->list);
- module_bug_cleanup(mod);
- return 0;
-}
-
#ifdef CONFIG_DEBUG_SET_MODULE_RONX
/*
* LKM RO/NX protection: protect module's text/ro-data
@@ -1860,7 +1848,11 @@ static void free_module(struct module *mod)

/* Now we can delete it from the lists */
mutex_lock(&module_mutex);
- stop_machine(__unlink_module, mod, NULL);
+ /* Unlink carefully: kallsyms could be walking list. */
+ list_del_rcu(&mod->list);
+ /* Wait for RCU synchronizing before releasing mod->list. */
+ synchronize_rcu();
+ module_bug_cleanup(mod);
mutex_unlock(&module_mutex);

/* This may be NULL, but that's OK */