linux-kernel - [PATCH 1/3] nsfs: add evict callback into struct proc_ns

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Message-Id: <1556692945-3996-2-git-send-email-wenbinzeng@tencent.com>
Date:   Wed,  1 May 2019 14:42:23 +0800
From:   Wenbin Zeng <wenbin.zeng@...il.com>
To:     viro@...iv.linux.org.uk, davem@...emloft.net, bfields@...ldses.org,
        jlayton@...nel.org, trond.myklebust@...merspace.com,
        anna.schumaker@...app.com, wenbinzeng@...cent.com,
        dsahern@...il.com, nicolas.dichtel@...nd.com, willy@...radead.org,
        edumazet@...gle.com, jakub.kicinski@...ronome.com,
        tyhicks@...onical.com, chuck.lever@...cle.com, neilb@...e.com
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-nfs@...r.kernel.org
Subject: [PATCH 1/3] nsfs: add evict callback into struct proc_ns_operations

The newly added evict callback shall be called by nsfs_evict(). Currently
only put() callback is called in nsfs_evict(), it is not able to release
all netns refcount, for example, a rpc client holds two netns refcounts,
these refcounts are supposed to be released when the rpc client is freed,
but the code to free rpc client is normally triggered by put() callback
only when netns refcount gets to 0, specifically:
    refcount=0 -> cleanup_net() -> ops_exit_list -> free rpc client
But netns refcount will never get to 0 before rpc client gets freed, to
break the deadlock, the code to free rpc client can be put into the newly
added evict callback.

Signed-off-by: Wenbin Zeng <wenbinzeng@...cent.com>
---
 fs/nsfs.c               | 2 ++
 include/linux/proc_ns.h | 1 +
 2 files changed, 3 insertions(+)

diff --git a/fs/nsfs.c b/fs/nsfs.c
index 60702d6..5939b12 100644
--- a/fs/nsfs.c
+++ b/fs/nsfs.c
@@ -49,6 +49,8 @@ static void nsfs_evict(struct inode *inode)
 	struct ns_common *ns = inode->i_private;
 	clear_inode(inode);
 	ns->ops->put(ns);
+	if (ns->ops->evict)
+		ns->ops->evict(ns);
 }
 
 static void *__ns_get_path(struct path *path, struct ns_common *ns)
diff --git a/include/linux/proc_ns.h b/include/linux/proc_ns.h
index d31cb62..919f0d4 100644
--- a/include/linux/proc_ns.h
+++ b/include/linux/proc_ns.h
@@ -19,6 +19,7 @@ struct proc_ns_operations {
 	int type;
 	struct ns_common *(*get)(struct task_struct *task);
 	void (*put)(struct ns_common *ns);
+	void (*evict)(struct ns_common *ns);
 	int (*install)(struct nsproxy *nsproxy, struct ns_common *ns);
 	struct user_namespace *(*owner)(struct ns_common *ns);
 	struct ns_common *(*get_parent)(struct ns_common *ns);
-- 
1.8.3.1