linux-kernel - Re: [PATCH] fs: handle shrinker registration failure in sget

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Message-Id: <201711232235.CDI34369.FLOtQVHFSJOOMF@I-love.SAKURA.ne.jp>
Date:   Thu, 23 Nov 2017 22:35:34 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     jack@...e.cz, mhocko@...nel.org
Cc:     viro@...iv.linux.org.uk, david@...morbit.com,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        akpm@...ux-foundation.org
Subject: Re: [PATCH] fs: handle shrinker registration failure in sget_userns

Jan Kara wrote:
> Looks good to me now. You can add:
> 
> Reviewed-by: Jan Kara <jack@...e.cz>
> 

It does not look good to me, for "goto fail" can call
destroy_unused_super() before s->s_shrink.list is initialized.
Also, the comment block saying "this object isn't exposed yet"
wants to be updated?

---
 fs/super.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index 80b118c..44f0c6b 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -197,6 +197,7 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
 	if (!s)
 		return NULL;
 
+	INIT_LIST_HEAD(&s->s_shrink.list);
 	INIT_LIST_HEAD(&s->s_mounts);
 	s->s_user_ns = get_user_ns(user_ns);
 
@@ -260,9 +261,8 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
 	s->s_shrink.count_objects = super_cache_count;
 	s->s_shrink.batch = 1024;
 	s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
-	INIT_LIST_HEAD(&s->s_shrink.list);
-	return s;
-
+	if (register_shrinker(&s->s_shrink) == 0)
+		return s;
 fail:
 	destroy_unused_super(s);
 	return NULL;
@@ -512,10 +512,6 @@ struct super_block *sget_userns(struct file_system_type *type,
 		s = alloc_super(type, (flags & ~SB_SUBMOUNT), user_ns);
 		if (!s)
 			return ERR_PTR(-ENOMEM);
-		if (register_shrinker(&s->s_shrink)) {
-			destroy_unused_super(s);
-			return ERR_PTR(-ENOMEM);
-		}
 		goto retry;
 	}
 
-- 
1.8.3.1