Once it is off the super_blocks list we don't really need to hold the
sb_lock anymore, we can defer the rest of the work. This reduces a few
uneeded operations from contention from the sb_lock.
This is a minor optimization found through code inspection. If the
sb_lock is not needed, no need for contention to wait while we free
items. While at it, add a bit of documentation about the extent to
which the sb_lock is used.
Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
---
fs/super.c | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)
diff --git a/fs/super.c b/fs/super.c
index bcef3a6f4c4b..24a76490c46f 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -43,6 +43,13 @@
static int thaw_super_locked(struct super_block *sb);
static LIST_HEAD(super_blocks);
+
+/**
+ * Protects the super_blocks list as well as the respective fs_type->fs_supers.
+ * When removing a super block it is first removed from the fs_type->fs_supers
+ * through generic_shutdown_super(). The final nail on the super block is the
+ * last temporary reference with __put_super().
+ */
static DEFINE_SPINLOCK(sb_lock);
static char *sb_writers_name[SB_FREEZE_LEVELS] = {
@@ -160,6 +167,11 @@ static void destroy_super_work(struct work_struct *work)
destroy_work);
int i;
+ security_sb_free(s);
+ fscrypt_sb_free(s);
+ put_user_ns(s->s_user_ns);
+ kfree(s->s_subtype);
+
for (i = 0; i < SB_FREEZE_LEVELS; i++)
percpu_free_rwsem(&s->s_writers.rw_sem[i]);
kfree(s);
@@ -292,10 +304,6 @@ static void __put_super(struct super_block *s)
WARN_ON(s->s_dentry_lru.node);
WARN_ON(s->s_inode_lru.node);
WARN_ON(!list_empty(&s->s_mounts));
- security_sb_free(s);
- fscrypt_sb_free(s);
- put_user_ns(s->s_user_ns);
- kfree(s->s_subtype);
call_rcu(&s->rcu, destroy_super_rcu);
}
}
@@ -471,7 +479,7 @@ void generic_shutdown_super(struct super_block *sb)
}
}
spin_lock(&sb_lock);
- /* should be initialized for __put_super_and_need_restart() */
+ /* and so __put_super() does not need to deal with this */
hlist_del_init(&sb->s_instances);
spin_unlock(&sb_lock);
up_write(&sb->s_umount);
--
2.30.2
