module: don't use stop_machine for waiting rmmod

rmmod has a little-used "-w" option, meaning that instead of failing if the
module is in use, it should block until the module becomes unused.

In this case, we don't need to use stop_machine: Max Krasnyansky
indicated that would be useful for SystemTap which loads/unloads new
modules frequently.

Cc: Max Krasnyansky <maxk@qualcomm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 11 insertions, 4 deletions

diff --git a/kernel/module.c b/kernel/module.c
index 5f80478b746d..705e1d5d516c 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -639,8 +639,8 @@ static int __try_stop_module(void *_sref)
 {
         struct stopref *sref = _sref;
 
-        /* If it's not unused, quit unless we are told to block. */
-        if ((sref->flags & O_NONBLOCK) && module_refcount(sref->mod) != 0) {
+        /* If it's not unused, quit unless we're forcing. */
+        if (module_refcount(sref->mod) != 0) {
                 if (!(*sref->forced = try_force_unload(sref->flags)))
                         return -EWOULDBLOCK;
         }
@@ -652,9 +652,16 @@ static int __try_stop_module(void *_sref)
 
 static int try_stop_module(struct module *mod, int flags, int *forced)
 {
-        struct stopref sref = { mod, flags, forced };
+        if (flags & O_NONBLOCK) {
+                struct stopref sref = { mod, flags, forced };
 
-        return stop_machine_run(__try_stop_module, &sref, NR_CPUS);
+                return stop_machine_run(__try_stop_module, &sref, NR_CPUS);
+        } else {
+                /* We don't need to stop the machine for this. */
+                mod->state = MODULE_STATE_GOING;
+                synchronize_sched();
+                return 0;
+        }
 }
 
 unsigned int module_refcount(struct module *mod)