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 d1d7c78..0c3bd95 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