linux-kernel - [PATCH v12 05/18] fs: do not use destroy_super() in alloc

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Date:	Mon, 2 Dec 2013 15:19:40 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	<hannes@...xchg.org>, <mhocko@...e.cz>, <dchinner@...hat.com>,
	<akpm@...ux-foundation.org>
CC:	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	<cgroups@...r.kernel.org>, <devel@...nvz.org>,
	<glommer@...nvz.org>, <vdavydov@...allels.com>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: [PATCH v12 05/18] fs: do not use destroy_super() in alloc_super() fail path

Using destroy_super() in alloc_super() fail path is bad, because:

* It will trigger WARN_ON(!list_empty(&s->s_mounts)) since s_mounts is
  initialized after several 'goto fail's.
* It will call kfree_rcu() to free the super block although kfree() is
  obviously enough there.
* The list_lru structure was initially implemented without the ability
  to destroy an uninitialized object in mind.

I'm going to replace the conventional list_lru with per-memcg lru to
implement per-memcg slab reclaim. This new structure will fail
destruction of objects that haven't been properly initialized so let's
inline appropriate snippets from destroy_super() to alloc_super() fail
path instead of using the whole function there.

Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
---
 fs/super.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index e5f6c2c..cece164 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -185,8 +185,10 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags)

 	if (list_lru_init(&s->s_dentry_lru))
 		goto fail;
-	if (list_lru_init(&s->s_inode_lru))
+	if (list_lru_init(&s->s_inode_lru)) {
+		list_lru_destroy(&s->s_dentry_lru);
 		goto fail;
+	}

 	INIT_LIST_HEAD(&s->s_mounts);
 	init_rwsem(&s->s_umount);
@@ -227,7 +229,10 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags)
 	return s;

 fail:
-	destroy_super(s);
+	for (i = 0; i < SB_FREEZE_LEVELS; i++)
+		percpu_counter_destroy(&s->s_writers.counter[i]);
+	security_sb_free(s);
+	kfree(s);
 	return NULL;
 }

-- 
1.7.10.4

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