lib/bug: Use RCU list ops for module_bug_list

Actually since module_bug_list should be used in BUG context,
we may not need this. But for someone who want to use this
from normal context, this makes module_bug_list an RCU list.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/kernel/module.c b/kernel/module.c
index bed608b..d596a30 100644 (file)
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1850,9 +1850,10 @@ static void free_module(struct module *mod)
        mutex_lock(&module_mutex);
        /* Unlink carefully: kallsyms could be walking list. */
        list_del_rcu(&mod->list);
-       /* Wait for RCU synchronizing before releasing mod->list. */
-       synchronize_rcu();
+       /* 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();
        mutex_unlock(&module_mutex);
 
        /* This may be NULL, but that's OK */

diff --git a/lib/bug.c b/lib/bug.c
index d1d7c78..0c3bd95 100644 (file)
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -64,16 +64,22 @@ static LIST_HEAD(module_bug_list);
 static const struct bug_entry *module_find_bug(unsigned long bugaddr)
 {
        struct module *mod;
+       const struct bug_entry *bug = NULL;
 
-       list_for_each_entry(mod, &module_bug_list, bug_list) {
-               const struct bug_entry *bug = mod->bug_table;
+       rcu_read_lock();
+       list_for_each_entry_rcu(mod, &module_bug_list, bug_list) {
                unsigned i;
 
+               bug = mod->bug_table;
                for (i = 0; i < mod->num_bugs; ++i, ++bug)
                        if (bugaddr == bug_addr(bug))
-                               return bug;
+                               goto out;
        }
-       return NULL;
+       bug = NULL;
+out:
+       rcu_read_unlock();
+
+       return bug;
 }
 
 void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
@@ -99,13 +105,15 @@ void module_bug_finalize(const Elf_Ehdr *hdr, const Elf_Shdr *sechdrs,
         * Strictly speaking this should have a spinlock to protect against
         * traversals, but since we only traverse on BUG()s, a spinlock
         * could potentially lead to deadlock and thus be counter-productive.
+        * Thus, this uses RCU to safely manipulate the bug list, since BUG
+        * must run in non-interruptive state.
         */
-       list_add(&mod->bug_list, &module_bug_list);
+       list_add_rcu(&mod->bug_list, &module_bug_list);
 }
 
 void module_bug_cleanup(struct module *mod)
 {
-       list_del(&mod->bug_list);
+       list_del_rcu(&mod->bug_list);
 }
 
 #else