Re: [PATCH] ceph: decease session->s_trim_caps only after caps get trimmed

[Jeff Layton <jlayton@redhat.com>]

On Thu, 2017-11-30 at 15:53 +0800, Yan, Zheng wrote:
> d_prune_aliases() does not prune dentry that has non-zero reference
> count. If we want trim_caps() to trim 'N' caps, the first 'N' inodes
> in session->s_caps are all directories with child dentry, trim_caps()
> can fail to trim anything.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
> ---
>  fs/ceph/mds_client.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
> index 80339e278ad8..da181acd4a61 100644
> --- a/fs/ceph/mds_client.c
> +++ b/fs/ceph/mds_client.c
> @@ -1490,16 +1490,20 @@ static int trim_caps_cb(struct inode *inode, struct ceph_cap *cap, void *arg)
>  	if ((used | wanted) & ~oissued & mine)
>  		goto out;   /* we need these caps */
>  
> -	session->s_trim_caps--;
>  	if (oissued) {
>  		/* we aren't the only cap.. just remove us */
>  		__ceph_remove_cap(cap, true);
> +		session->s_trim_caps--;
>  	} else {
> +		int refs;
>  		/* try dropping referring dentries */
>  		spin_unlock(&ci->i_ceph_lock);
>  		d_prune_aliases(inode);
> +		refs = atomic_read(&inode->i_count);
> +		if (refs == 1)
> +			session->s_trim_caps--;
>  		dout("trim_caps_cb %p cap %p  pruned, count now %d\n",
> -		     inode, cap, atomic_read(&inode->i_count));
> +		     inode, cap, refs);
>  		return 0;
>  	}
>  

Reviewed-by: Jeff Layton <jlayton@redhat.com>