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Subject: [PATCH RFC 05/10] fs: Move list_lru_destroy() to
 destroy_super_work()
From:   Kirill Tkhai <ktkhai@virtuozzo.com>
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Date:   Tue, 07 Aug 2018 18:38:23 +0300
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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 {