module: weaken locking assertion for oops path.

We don't actually hold the module_mutex when calling find_module_all
from module_kallsyms_lookup_name: that's because it's used by the oops
code and we don't want to deadlock.

However, access to the list read-only is safe if preempt is disabled,
so we can weaken the assertion.  Keep a strong version for external
callers though.

Fixes: 0be964be0d45 ("module: Sanitize RCU usage and locking")
Reported-by: He Kuang <hekuang@huawei.com>
Cc: stable@kernel.org
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/kernel/module.c b/kernel/module.c
index 4d2b82e610e2a48f429a700f0529d6dc5942700a..b86b7bf1be388d72fe92fb6038b4a67b4710df1f 100644 (file)
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -602,13 +602,16 @@ const struct kernel_symbol *find_symbol(const char *name,
 }
 EXPORT_SYMBOL_GPL(find_symbol);
 
-/* Search for module by name: must hold module_mutex. */
+/*
+ * Search for module by name: must hold module_mutex (or preempt disabled
+ * for read-only access).
+ */
 static struct module *find_module_all(const char *name, size_t len,
                                      bool even_unformed)
 {
        struct module *mod;
 
-       module_assert_mutex();
+       module_assert_mutex_or_preempt();
 
        list_for_each_entry(mod, &modules, list) {
                if (!even_unformed && mod->state == MODULE_STATE_UNFORMED)
@@ -621,6 +624,7 @@ static struct module *find_module_all(const char *name, size_t len,
 
 struct module *find_module(const char *name)
 {
+       module_assert_mutex();
        return find_module_all(name, strlen(name), false);
 }
 EXPORT_SYMBOL_GPL(find_module);