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>

1 files changed, 14 insertions, 6 deletions

diff --git a/lib/bug.c b/lib/bug.c
index d1d7c7878900..0c3bd9552b6f 100644
--- 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