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SubjectRe: [PATCH 1/3] nsfs: add evict callback into struct proc_ns_operations
On Wed, May 01, 2019 at 02:42:23PM +0800, Wenbin Zeng wrote:
> 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@tencent.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);

What's to guarantee that ns will not be freed by ->put()?
Confused...

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