[PATCH v2 10/28] module: Use RCU in find_symbol().

[Sebastian Andrzej Siewior]

module_assert_mutex_or_preempt() is not needed in find_symbol(). The
function checks for RCU-sched or the module_mutex to be acquired. The
list_for_each_entry_rcu() below does the same check.

Remove module_assert_mutex_or_preempt() from try_add_tainted_module().
Use RCU protection to invoke find_symbol() and update callers.

Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
---
 kernel/module/main.c    | 30 ++++++++++++------------------
 kernel/module/version.c | 14 +++++++-------
 2 files changed, 19 insertions(+), 25 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index 5aa56ec8e203e..71e73deed76c0 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -331,7 +331,7 @@ static bool find_exported_symbol_in_section(const struct 
symsearch *syms,
 
 /*
  * Find an exported symbol and return it, along with, (optional) crc and
- * (optional) module which owns it.  Needs preempt disabled or module_mutex.
+ * (optional) module which owns it. Needs RCU or module_mutex.
  */
 bool find_symbol(struct find_symbol_arg *fsa)
 {
@@ -345,8 +345,6 @@ bool find_symbol(struct find_symbol_arg *fsa)
        struct module *mod;
        unsigned int i;
 
-       module_assert_mutex_or_preempt();
-
        for (i = 0; i < ARRAY_SIZE(arr); i++)
                if (find_exported_symbol_in_section(&arr[i], NULL, fsa))
                        return true;
@@ -812,10 +810,9 @@ void __symbol_put(const char *symbol)
                .gplok  = true,
        };
 
-       preempt_disable();
+       guard(rcu)();
        BUG_ON(!find_symbol(&fsa));
        module_put(fsa.owner);
-       preempt_enable();
 }
 EXPORT_SYMBOL(__symbol_put);
 
@@ -1369,21 +1366,18 @@ void *__symbol_get(const char *symbol)
                .warn   = true,
        };
 
-       preempt_disable();
-       if (!find_symbol(&fsa))
-               goto fail;
-       if (fsa.license != GPL_ONLY) {
-               pr_warn("failing symbol_get of non-GPLONLY symbol %s.\n",
-                       symbol);
-               goto fail;
+       scoped_guard(rcu) {
+               if (!find_symbol(&fsa))
+                       return NULL;
+               if (fsa.license != GPL_ONLY) {
+                       pr_warn("failing symbol_get of non-GPLONLY symbol 
%s.\n",
+                               symbol);
+                       return NULL;
+               }
+               if (strong_try_module_get(fsa.owner))
+                       return NULL;
        }
-       if (strong_try_module_get(fsa.owner))
-               goto fail;
-       preempt_enable();
        return (void *)kernel_symbol_value(fsa.sym);
-fail:
-       preempt_enable();
-       return NULL;
 }
 EXPORT_SYMBOL_GPL(__symbol_get);
 
diff --git a/kernel/module/version.c b/kernel/module/version.c
index 53f43ac5a73e9..65ef8f2a821da 100644
--- a/kernel/module/version.c
+++ b/kernel/module/version.c
@@ -62,17 +62,17 @@ int check_modstruct_version(const struct load_info *info,
                .name   = "module_layout",
                .gplok  = true,
        };
+       bool have_symbol;
 
        /*
         * Since this should be found in kernel (which can't be removed), no
-        * locking is necessary -- use preempt_disable() to placate lockdep.
+        * locking is necessary. Regardless use a RCU read section to keep
+        * lockdep happy.
         */
-       preempt_disable();
-       if (!find_symbol(&fsa)) {
-               preempt_enable();
-               BUG();
-       }
-       preempt_enable();
+       scoped_guard(rcu)
+               have_symbol = find_symbol(&fsa);
+       BUG_ON(!have_symbol);
+
        return check_version(info, "module_layout", mod, fsa.crc);
 }
 
-- 
2.45.2