Messages in this thread Patch in this message | | | Subject | Re: [PATCH 1/2] module: use rcu to protect module list read | From | Eric Dumazet <> | Date | Sat, 10 Mar 2012 07:25:57 -0800 |
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Le samedi 10 mars 2012 à 22:20 +0800, Cong Wang a écrit : > Now the read of module list is protected by preempt disable + *_rcu > list operations, this is odd, as RCU read lock should be able to > protect it directly. This patch makes the read of module list > protected by RCU read lock and the write still protected by > module_mutex. >
Problem is that your patch does more than that.
In set_all_modules_text_rw() and set_all_modules_text_ro() you removed the mutex in favor of rcu_read_lock()
Also, module code uses synchronize_sched(), not synchronize_rcu()
Take a look at Documentation/RCU/whatisRCU.txt and see that preempt_disable() / preempt_enable() are documented as a right protect code, in line 333.
You added races in /proc/modules as well.
So I would say your patch is not needed at all : module code already uses RCU.
What particular problem do you have with current code ?
I would probably do the opposite patch, since its clear that at least in two points we use the wrong macro :
diff --git a/kernel/module.c b/kernel/module.c index 2c93276..cacb36e 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -1714,7 +1714,7 @@ void set_all_modules_text_rw(void) struct module *mod; mutex_lock(&module_mutex); - list_for_each_entry_rcu(mod, &modules, list) { + list_for_each_entry(mod, &modules, list) { if ((mod->module_core) && (mod->core_text_size)) { set_page_attributes(mod->module_core, mod->module_core + mod->core_text_size, @@ -1735,7 +1735,7 @@ void set_all_modules_text_ro(void) struct module *mod; mutex_lock(&module_mutex); - list_for_each_entry_rcu(mod, &modules, list) { + list_for_each_entry(mod, &modules, list) { if ((mod->module_core) && (mod->core_text_size)) { set_page_attributes(mod->module_core, mod->module_core + mod->core_text_size,
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