[PATCH RFC 05/10] fs: Move list_lru_destroy() to destroy_super_work()

Kirill Tkhai
2018-08-07T15:38:45Z

The patch makes s_dentry_lru and s_inode_lru be destroyed
later from the workqueue. This is preparation to split
unregister_shrinker(super_block::s_shrink) in two stages,
and to call finalize stage from destroy_super_work().

Note, that generic filesystem shrinker unregistration
is safe to be splitted in two stages right after this
patch, since super_cache_count() and super_cache_scan()
have a deal with s_dentry_lru and s_inode_lru only.

But there are two exceptions: XFS and SHMEM, which
define .nr_cached_objects() and .free_cached_objects()
callbacks. These two do not allow us to do the splitting
right after this patch. They touch fs-specific data,
which is destroyed earlier, than destroy_super_work().
So, we can't call unregister_shrinker_delayed_finalize()
from destroy_super_work() because of them, and next
patches make preparations to make this possible.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
fs/super.c | 17 +++++------------
1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index 426161360af3..457834278e37 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -159,6 +159,11 @@ static void destroy_super_work(struct work_struct *work)
destroy_work);
int i;

+ WARN_ON(list_lru_count(&s->s_dentry_lru));
+ WARN_ON(list_lru_count(&s->s_inode_lru));
+ list_lru_destroy(&s->s_dentry_lru);
+ list_lru_destroy(&s->s_inode_lru);
+
for (i = 0; i < SB_FREEZE_LEVELS; i++)
percpu_free_rwsem(&s->s_writers.rw_sem[i]);
kfree(s);
@@ -177,8 +182,6 @@ static void destroy_unused_super(struct super_block *s)
if (!s)
return;
up_write(&s->s_umount);
- list_lru_destroy(&s->s_dentry_lru);
- list_lru_destroy(&s->s_inode_lru);
security_sb_free(s);
put_user_ns(s->s_user_ns);
kfree(s->s_subtype);
@@ -283,8 +286,6 @@ static void __put_super(struct super_block *s)
{
if (!--s->s_count) {
list_del_init(&s->s_list);
- 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);
put_user_ns(s->s_user_ns);
@@ -327,14 +328,6 @@ void deactivate_locked_super(struct super_block *s)
unregister_shrinker(&s->s_shrink);
fs->kill_sb(s);

- /*
- * Since list_lru_destroy() may sleep, we cannot call it from
- * put_super(), where we hold the sb_lock. Therefore we destroy
- * the lru lists right now.
- */
- list_lru_destroy(&s->s_dentry_lru);
- list_lru_destroy(&s->s_inode_lru);
-
put_filesystem(fs);
put_super(s);
} else {