fs: fix ups and tidy ups to /proc/filesystems caching

- add missing unlocks in some corner cases
- whitespace touch ups
- s/smp_store_release/rcu_assign_pointer/ [nop, the macro expands to the same thing]
- mark file_systems_string as __read_mostly

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://patch.msgid.link/20260610143954.34185-1-mjguzik@gmail.com
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

diff --git a/fs/filesystems.c b/fs/filesystems.c
index 771fc31a69b8fbec4420b72d144c60d060564bd8..673a03b5f32b437e667ec83a9fb499026910ba00 100644 (file)
--- a/fs/filesystems.c
+++ b/fs/filesystems.c
@@ -54,7 +54,7 @@ struct file_systems_string {
 };
 
 static unsigned long file_systems_gen;
-static struct file_systems_string __rcu *file_systems_string;
+static struct file_systems_string __read_mostly __rcu *file_systems_string;
 
 static void invalidate_filesystems_string(void);
 #else
@@ -269,7 +269,7 @@ retry:
        hlist_for_each_entry_rcu(p, &file_systems, list) {
                if (!(p->fs_flags & FS_REQUIRES_DEV))
                        newlen += strlen("nodev");
-               newlen += strlen("\t") + strlen(p->name) +  strlen("\n");
+               newlen += strlen("\t") + strlen(p->name) + strlen("\n");
        }
        spin_unlock(&file_systems_lock);
 
@@ -289,6 +289,7 @@ retry:
         * Did someone beat us to it?
         */
        if (old && old->gen == file_systems_gen) {
+               spin_unlock(&file_systems_lock);
                kfree(new);
                return 0;
        }
@@ -297,6 +298,7 @@ retry:
         * Did the list change in the meantime?
         */
        if (gen != file_systems_gen) {
+               spin_unlock(&file_systems_lock);
                kfree(new);
                goto retry;
        }
@@ -321,15 +323,11 @@ retry:
                 * generation above and messes it up.
                 */
                spin_unlock(&file_systems_lock);
-               if (old)
-                       kfree_rcu(old, rcu);
+               kfree(new);
                return -EINVAL;
        }
 
-       /*
-        * Paired with consume fence in READ_ONCE() in filesystems_proc_show()
-        */
-       smp_store_release(&file_systems_string, new);
+       rcu_assign_pointer(file_systems_string, new);
        spin_unlock(&file_systems_lock);
        if (old)
                kfree_rcu(old, rcu);