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

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On Fri, Nov 17, 2023 at 11:19:51AM +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.
> 
> Switch to use the 'dget_parent()' to get the parent dentry and also
> keep holding the parent until the corresponding inode is not being
> refereenced.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> URL: https://www.spinics.net/lists/ceph-devel/msg58622.html
> Fixes: adf0d68701c7 ("ceph: fix unsafe dcache access in ceph_encode_dentry_release")
> Cc: Jeff Layton <jlayton@xxxxxxxxxx>
> Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>

> +	if (!dir) {
> +		parent = dget_parent(dentry);
> +		dir = d_inode(parent);
> +	}

It's never actually called with dir == NULL.  Not since 2016.

All you need is this, _maybe_ with BUG_ON(!dir); added in the beginning of the function.

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 2c0b8dc3dd0d..22d6ea97938f 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -4887,7 +4887,6 @@ 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;
@@ -4903,14 +4902,9 @@ 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);



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