Re: [PATCH v2] ceph: fix deadlock or deadcode of misusing dget()

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On Fri, 2023-11-17 at 13:36 +0800, xiubli@xxxxxxxxxx wrote:
> From: Xiubo Li <xiubli@xxxxxxxxxx>
> 
> The lock order is incorrect between denty and its parent, we should
> always make sure that the parent get the lock first.
> 
> But since this deadcode is never used and the parent dir will always
> be set from the callers, let's just remove it.
> 
> Reported-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> URL: https://www.spinics.net/lists/ceph-devel/msg58622.html
> Cc: Jeff Layton <jlayton@xxxxxxxxxx>
> Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
> ---
> 
> 
> V2:
> - Just remove the deadcode. Actually this just removed the deadcode,
>   not fixing any deadlock issue and I also just removed ccing the
>   stable list.
> 
> 
>  fs/ceph/caps.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
> index 284424659329..a9e19f1f26e0 100644
> --- a/fs/ceph/caps.c
> +++ b/fs/ceph/caps.c
> @@ -4916,13 +4916,15 @@ int ceph_encode_dentry_release(void **p, struct dentry *dentry,
>  			       struct inode *dir,
>  			       int mds, int drop, int unless)
>  {
> -	struct dentry *parent = NULL;
>  	struct ceph_mds_request_release *rel = *p;
>  	struct ceph_dentry_info *di = ceph_dentry(dentry);
>  	struct ceph_client *cl;
>  	int force = 0;
>  	int ret;
>  
> +	/* This shouldn't happen */
> +	BUG_ON(!dir);
> +
>  	/*
>  	 * force an record for the directory caps if we have a dentry lease.
>  	 * this is racy (can't take i_ceph_lock and d_lock together), but it
> @@ -4932,14 +4934,9 @@ int ceph_encode_dentry_release(void **p, struct dentry *dentry,
>  	spin_lock(&dentry->d_lock);
>  	if (di->lease_session && di->lease_session->s_mds == mds)
>  		force = 1;
> -	if (!dir) {
> -		parent = dget(dentry->d_parent);
> -		dir = d_inode(parent);
> -	}
>  	spin_unlock(&dentry->d_lock);
>  
>  	ret = ceph_encode_inode_release(p, dir, mds, drop, unless, force);
> -	dput(parent);
>  
>  	cl = ceph_inode_to_client(dir);
>  	spin_lock(&dentry->d_lock);

Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>





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