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From:   Christian Schoenebeck <linux_oss@crudebyte.com>
To:     Eric Van Hensbergen <ericvh@gmail.com>,
        Latchesar Ionkov <lucho@ionkov.net>,
        Dominique Martinet <asmadeus@codewreck.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Tyler Hicks <tyhicks@linux.microsoft.com>
Cc:     v9fs-developer@lists.sourceforge.net, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org
Subject: Re: [PATCH v3 04/06] 9p fid refcount: add p9_fid_get/put wrappers
Date:   Wed, 15 Jun 2022 15:00:19 +0200
Message-ID: <21498866.auqpVWlHDa@silver>
In-Reply-To: <20220615031647.1764797-1-asmadeus@codewreck.org>
References: <7044959.MN0D2SvuAq@silver> <20220615031647.1764797-1-asmadeus@codewreck.org>
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Precedence: bulk

On Mittwoch, 15. Juni 2022 05:16:45 CEST Dominique Martinet wrote:
> I was recently reminded that it is not clear that p9_client_clunk()
> was actually just decrementing refcount and clunking only when that
> reaches zero: make it clear through a set of helpers.
> 
> This will also allow instrumenting refcounting better for debugging
> next patch
> 
> Link:
> https://lkml.kernel.org/r/20220612085330.1451496-5-asmadeus@codewreck.org
> Reviewed-by: Tyler Hicks <tyhicks@linux.microsoft.com>
> Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
> ---
> v1 -> v2: p9_fid_get/put are now static inline in .h
> v2 -> v3: fix commit message and add comment to helpers
> 
>  fs/9p/fid.c             | 18 ++++++++--------
>  fs/9p/fid.h             |  2 +-
>  fs/9p/vfs_addr.c        |  4 ++--
>  fs/9p/vfs_dentry.c      |  4 ++--
>  fs/9p/vfs_dir.c         |  2 +-
>  fs/9p/vfs_file.c        |  4 ++--
>  fs/9p/vfs_inode.c       | 48 ++++++++++++++++++++---------------------
>  fs/9p/vfs_inode_dotl.c  | 42 ++++++++++++++++++------------------
>  fs/9p/vfs_super.c       |  6 +++---
>  fs/9p/xattr.c           |  8 +++----
>  include/net/9p/client.h | 28 ++++++++++++++++++++++++
>  net/9p/client.c         | 15 +++----------
>  12 files changed, 100 insertions(+), 81 deletions(-)
> 
> diff --git a/fs/9p/fid.c b/fs/9p/fid.c
> index e8fad28fc5bd..d792499349c4 100644
> --- a/fs/9p/fid.c
> +++ b/fs/9p/fid.c
> @@ -56,7 +56,7 @@ static struct p9_fid *v9fs_fid_find_inode(struct inode
> *inode, kuid_t uid) h = (struct hlist_head *)&inode->i_private;
>  	hlist_for_each_entry(fid, h, ilist) {
>  		if (uid_eq(fid->uid, uid)) {
> -			refcount_inc(&fid->count);
> +			p9_fid_get(fid);
>  			ret = fid;
>  			break;
>  		}
> @@ -104,7 +104,7 @@ static struct p9_fid *v9fs_fid_find(struct dentry
> *dentry, kuid_t uid, int any) hlist_for_each_entry(fid, h, dlist) {
>  			if (any || uid_eq(fid->uid, uid)) {
>  				ret = fid;
> -				refcount_inc(&ret->count);
> +				p9_fid_get(ret);
>  				break;
>  			}
>  		}
> @@ -172,7 +172,7 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct
> dentry *dentry, old_fid = fid;
> 
>  		fid = p9_client_walk(old_fid, 1, &dentry->d_name.name, 1);
> -		p9_client_clunk(old_fid);
> +		p9_fid_put(old_fid);
>  		goto fid_out;
>  	}
>  	up_read(&v9ses->rename_sem);
> @@ -194,7 +194,7 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct
> dentry *dentry, if (IS_ERR(root_fid))
>  			return root_fid;
> 
> -		refcount_inc(&root_fid->count);
> +		p9_fid_get(root_fid);
>  		v9fs_fid_add(dentry->d_sb->s_root, root_fid);
>  	}
>  	/* If we are root ourself just return that */
> @@ -225,7 +225,7 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct
> dentry *dentry, old_fid == root_fid /* clone */);
>  		/* non-cloning walk will return the same fid */
>  		if (fid != old_fid) {
> -			p9_client_clunk(old_fid);
> +			p9_fid_put(old_fid);
>  			old_fid = fid;
>  		}
>  		if (IS_ERR(fid)) {
> @@ -240,11 +240,11 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct
> dentry *dentry, spin_lock(&dentry->d_lock);
>  		if (d_unhashed(dentry)) {
>  			spin_unlock(&dentry->d_lock);
> -			p9_client_clunk(fid);
> +			p9_fid_put(fid);
>  			fid = ERR_PTR(-ENOENT);
>  		} else {
>  			__add_fid(dentry, fid);
> -			refcount_inc(&fid->count);
> +			p9_fid_get(fid);
>  			spin_unlock(&dentry->d_lock);
>  		}
>  	}
> @@ -301,7 +301,7 @@ struct p9_fid *v9fs_writeback_fid(struct dentry *dentry)
> fid = clone_fid(ofid);
>  	if (IS_ERR(fid))
>  		goto error_out;
> -	p9_client_clunk(ofid);
> +	p9_fid_put(ofid);
>  	/*
>  	 * writeback fid will only be used to write back the
>  	 * dirty pages. We always request for the open fid in read-write
> @@ -310,7 +310,7 @@ struct p9_fid *v9fs_writeback_fid(struct dentry *dentry)
> */
>  	err = p9_client_open(fid, O_RDWR);
>  	if (err < 0) {
> -		p9_client_clunk(fid);
> +		p9_fid_put(fid);
>  		fid = ERR_PTR(err);
>  		goto error_out;
>  	}
> diff --git a/fs/9p/fid.h b/fs/9p/fid.h
> index f7f33509e169..3168dfad510e 100644
> --- a/fs/9p/fid.h
> +++ b/fs/9p/fid.h
> @@ -29,7 +29,7 @@ static inline struct p9_fid *v9fs_fid_clone(struct dentry
> *dentry) return fid;
> 
>  	nfid = clone_fid(fid);
> -	p9_client_clunk(fid);
> +	p9_fid_put(fid);
>  	return nfid;
>  }
>  #endif
> diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c
> index 7f924e671e3e..c5f71eeb28b6 100644
> --- a/fs/9p/vfs_addr.c
> +++ b/fs/9p/vfs_addr.c
> @@ -70,7 +70,7 @@ static int v9fs_init_request(struct netfs_io_request
> *rreq, struct file *file)
> 
>  	BUG_ON(!fid);
> 
> -	refcount_inc(&fid->count);
> +	p9_fid_get(fid);
>  	rreq->netfs_priv = fid;
>  	return 0;
>  }
> @@ -83,7 +83,7 @@ static void v9fs_free_request(struct netfs_io_request
> *rreq) {
>  	struct p9_fid *fid = rreq->netfs_priv;
> 
> -	p9_client_clunk(fid);
> +	p9_fid_put(fid);
>  }
> 
>  /**
> diff --git a/fs/9p/vfs_dentry.c b/fs/9p/vfs_dentry.c
> index 1c609e99d280..f89f01734587 100644
> --- a/fs/9p/vfs_dentry.c
> +++ b/fs/9p/vfs_dentry.c
> @@ -54,7 +54,7 @@ static void v9fs_dentry_release(struct dentry *dentry)
>  	p9_debug(P9_DEBUG_VFS, " dentry: %pd (%p)\n",
>  		 dentry, dentry);
>  	hlist_for_each_safe(p, n, (struct hlist_head *)&dentry->d_fsdata)
> -		p9_client_clunk(hlist_entry(p, struct p9_fid, dlist));
> +		p9_fid_put(hlist_entry(p, struct p9_fid, dlist));
>  	dentry->d_fsdata = NULL;
>  }
> 
> @@ -85,7 +85,7 @@ static int v9fs_lookup_revalidate(struct dentry *dentry,
> unsigned int flags) retval = v9fs_refresh_inode_dotl(fid, inode);
>  		else
>  			retval = v9fs_refresh_inode(fid, inode);
> -		p9_client_clunk(fid);
> +		p9_fid_put(fid);
> 
>  		if (retval == -ENOENT)
>  			return 0;
> diff --git a/fs/9p/vfs_dir.c b/fs/9p/vfs_dir.c
> index 958680f7f23e..000fbaae9b18 100644
> --- a/fs/9p/vfs_dir.c
> +++ b/fs/9p/vfs_dir.c
> @@ -218,7 +218,7 @@ int v9fs_dir_release(struct inode *inode, struct file
> *filp) spin_lock(&inode->i_lock);
>  		hlist_del(&fid->ilist);
>  		spin_unlock(&inode->i_lock);
> -		p9_client_clunk(fid);
> +		p9_fid_put(fid);
>  	}
> 
>  	if ((filp->f_mode & FMODE_WRITE)) {
> diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
> index 2573c08f335c..8276f3af35d7 100644
> --- a/fs/9p/vfs_file.c
> +++ b/fs/9p/vfs_file.c
> @@ -63,7 +63,7 @@ int v9fs_file_open(struct inode *inode, struct file *file)
> 
>  		err = p9_client_open(fid, omode);
>  		if (err < 0) {
> -			p9_client_clunk(fid);
> +			p9_fid_put(fid);
>  			return err;
>  		}
>  		if ((file->f_flags & O_APPEND) &&
> @@ -98,7 +98,7 @@ int v9fs_file_open(struct inode *inode, struct file *file)
> v9fs_open_fid_add(inode, fid);
>  	return 0;
>  out_error:
> -	p9_client_clunk(file->private_data);
> +	p9_fid_put(file->private_data);
>  	file->private_data = NULL;
>  	return err;
>  }
> diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
> index 3d8297714772..bde18776f0c7 100644
> --- a/fs/9p/vfs_inode.c
> +++ b/fs/9p/vfs_inode.c
> @@ -400,7 +400,7 @@ void v9fs_evict_inode(struct inode *inode)
>  	fscache_relinquish_cookie(v9fs_inode_cookie(v9inode), false);
>  	/* clunk the fid stashed in writeback_fid */
>  	if (v9inode->writeback_fid) {
> -		p9_client_clunk(v9inode->writeback_fid);
> +		p9_fid_put(v9inode->writeback_fid);
>  		v9inode->writeback_fid = NULL;
>  	}
>  }
> @@ -569,7 +569,7 @@ static int v9fs_remove(struct inode *dir, struct dentry
> *dentry, int flags) if (v9fs_proto_dotl(v9ses))
>  		retval = p9_client_unlinkat(dfid, dentry->d_name.name,
>  					    
v9fs_at_to_dotl_flags(flags));
> -	p9_client_clunk(dfid);
> +	p9_fid_put(dfid);
>  	if (retval == -EOPNOTSUPP) {
>  		/* Try the one based on path */
>  		v9fid = v9fs_fid_clone(dentry);
> @@ -633,14 +633,14 @@ v9fs_create(struct v9fs_session_info *v9ses, struct
> inode *dir, if (IS_ERR(ofid)) {
>  		err = PTR_ERR(ofid);
>  		p9_debug(P9_DEBUG_VFS, "p9_client_walk failed %d\n", err);
> -		p9_client_clunk(dfid);
> +		p9_fid_put(dfid);
>  		return ERR_PTR(err);
>  	}
> 
>  	err = p9_client_fcreate(ofid, name, perm, mode, extension);
>  	if (err < 0) {
>  		p9_debug(P9_DEBUG_VFS, "p9_client_fcreate failed %d\n", 
err);
> -		p9_client_clunk(dfid);
> +		p9_fid_put(dfid);
>  		goto error;
>  	}
> 
> @@ -652,7 +652,7 @@ v9fs_create(struct v9fs_session_info *v9ses, struct
> inode *dir, p9_debug(P9_DEBUG_VFS,
>  				   "p9_client_walk failed %d\n", err);
>  			fid = NULL;
> -			p9_client_clunk(dfid);
> +			p9_fid_put(dfid);
>  			goto error;
>  		}
>  		/*
> @@ -663,20 +663,20 @@ v9fs_create(struct v9fs_session_info *v9ses, struct
> inode *dir, err = PTR_ERR(inode);
>  			p9_debug(P9_DEBUG_VFS,
>  				   "inode creation failed %d\n", err);
> -			p9_client_clunk(dfid);
> +			p9_fid_put(dfid);
>  			goto error;
>  		}
>  		v9fs_fid_add(dentry, fid);
>  		d_instantiate(dentry, inode);
>  	}
> -	p9_client_clunk(dfid);
> +	p9_fid_put(dfid);
>  	return ofid;
>  error:
>  	if (ofid)
> -		p9_client_clunk(ofid);
> +		p9_fid_put(ofid);
> 
>  	if (fid)
> -		p9_client_clunk(fid);
> +		p9_fid_put(fid);
> 
>  	return ERR_PTR(err);
>  }
> @@ -708,7 +708,7 @@ v9fs_vfs_create(struct user_namespace *mnt_userns,
> struct inode *dir, return PTR_ERR(fid);
> 
>  	v9fs_invalidate_inode_attr(dir);
> -	p9_client_clunk(fid);
> +	p9_fid_put(fid);
> 
>  	return 0;
>  }
> @@ -744,7 +744,7 @@ static int v9fs_vfs_mkdir(struct user_namespace
> *mnt_userns, struct inode *dir, }
> 
>  	if (fid)
> -		p9_client_clunk(fid);
> +		p9_fid_put(fid);
> 
>  	return err;
>  }
> @@ -785,7 +785,7 @@ struct dentry *v9fs_vfs_lookup(struct inode *dir, struct
> dentry *dentry, */
>  	name = dentry->d_name.name;
>  	fid = p9_client_walk(dfid, 1, &name, 1);
> -	p9_client_clunk(dfid);
> +	p9_fid_put(dfid);
>  	if (fid == ERR_PTR(-ENOENT))
>  		inode = NULL;
>  	else if (IS_ERR(fid))
> @@ -808,7 +808,7 @@ struct dentry *v9fs_vfs_lookup(struct inode *dir, struct
> dentry *dentry, else if (!IS_ERR(res))
>  			v9fs_fid_add(res, fid);
>  		else
> -			p9_client_clunk(fid);
> +			p9_fid_put(fid);
>  	}
>  	return res;
>  }
> @@ -891,7 +891,7 @@ v9fs_vfs_atomic_open(struct inode *dir, struct dentry
> *dentry,
> 
>  error:
>  	if (fid)
> -		p9_client_clunk(fid);
> +		p9_fid_put(fid);
>  	goto out;
>  }
> 
> @@ -959,7 +959,7 @@ v9fs_vfs_rename(struct user_namespace *mnt_userns,
> struct inode *old_dir, dfid = v9fs_parent_fid(old_dentry);
>  	olddirfid = clone_fid(dfid);
>  	if (dfid && !IS_ERR(dfid))
> -		p9_client_clunk(dfid);
> +		p9_fid_put(dfid);
> 
>  	if (IS_ERR(olddirfid)) {
>  		retval = PTR_ERR(olddirfid);
> @@ -968,7 +968,7 @@ v9fs_vfs_rename(struct user_namespace *mnt_userns,
> struct inode *old_dir,
> 
>  	dfid = v9fs_parent_fid(new_dentry);
>  	newdirfid = clone_fid(dfid);
> -	p9_client_clunk(dfid);
> +	p9_fid_put(dfid);
> 
>  	if (IS_ERR(newdirfid)) {
>  		retval = PTR_ERR(newdirfid);
> @@ -1020,13 +1020,13 @@ v9fs_vfs_rename(struct user_namespace *mnt_userns,
> struct inode *old_dir, d_move(old_dentry, new_dentry);
>  	}
>  	up_write(&v9ses->rename_sem);
> -	p9_client_clunk(newdirfid);
> +	p9_fid_put(newdirfid);
> 
>  clunk_olddir:
> -	p9_client_clunk(olddirfid);
> +	p9_fid_put(olddirfid);
> 
>  done:
> -	p9_client_clunk(oldfid);
> +	p9_fid_put(oldfid);
>  	return retval;
>  }
> 
> @@ -1060,7 +1060,7 @@ v9fs_vfs_getattr(struct user_namespace *mnt_userns,
> const struct path *path, return PTR_ERR(fid);
> 
>  	st = p9_client_stat(fid);
> -	p9_client_clunk(fid);
> +	p9_fid_put(fid);
>  	if (IS_ERR(st))
>  		return PTR_ERR(st);
> 
> @@ -1136,7 +1136,7 @@ static int v9fs_vfs_setattr(struct user_namespace
> *mnt_userns, retval = p9_client_wstat(fid, &wstat);
> 
>  	if (use_dentry)
> -		p9_client_clunk(fid);
> +		p9_fid_put(fid);
> 
>  	if (retval < 0)
>  		return retval;
> @@ -1261,7 +1261,7 @@ static const char *v9fs_vfs_get_link(struct dentry
> *dentry, return ERR_CAST(fid);
> 
>  	st = p9_client_stat(fid);
> -	p9_client_clunk(fid);
> +	p9_fid_put(fid);
>  	if (IS_ERR(st))
>  		return ERR_CAST(st);
> 
> @@ -1308,7 +1308,7 @@ static int v9fs_vfs_mkspecial(struct inode *dir,
> struct dentry *dentry, return PTR_ERR(fid);
> 
>  	v9fs_invalidate_inode_attr(dir);
> -	p9_client_clunk(fid);
> +	p9_fid_put(fid);
>  	return 0;
>  }
> 
> @@ -1364,7 +1364,7 @@ v9fs_vfs_link(struct dentry *old_dentry, struct inode
> *dir, v9fs_refresh_inode(oldfid, d_inode(old_dentry));
>  		v9fs_invalidate_inode_attr(dir);
>  	}
> -	p9_client_clunk(oldfid);
> +	p9_fid_put(oldfid);
>  	return retval;
>  }
> 
> diff --git a/fs/9p/vfs_inode_dotl.c b/fs/9p/vfs_inode_dotl.c
> index b6eb1160296c..09b124fe349c 100644
> --- a/fs/9p/vfs_inode_dotl.c
> +++ b/fs/9p/vfs_inode_dotl.c
> @@ -274,7 +274,7 @@ v9fs_vfs_atomic_open_dotl(struct inode *dir, struct
> dentry *dentry, if (IS_ERR(ofid)) {
>  		err = PTR_ERR(ofid);
>  		p9_debug(P9_DEBUG_VFS, "p9_client_walk failed %d\n", err);
> -		p9_client_clunk(dfid);
> +		p9_fid_put(dfid);
>  		goto out;
>  	}
> 
> @@ -286,7 +286,7 @@ v9fs_vfs_atomic_open_dotl(struct inode *dir, struct
> dentry *dentry, if (err) {
>  		p9_debug(P9_DEBUG_VFS, "Failed to get acl values in creat 
%d\n",
>  			 err);
> -		p9_client_clunk(dfid);
> +		p9_fid_put(dfid);
>  		goto error;
>  	}
>  	err = p9_client_create_dotl(ofid, name, 
v9fs_open_to_dotl_flags(flags),
> @@ -294,14 +294,14 @@ v9fs_vfs_atomic_open_dotl(struct inode *dir, struct
> dentry *dentry, if (err < 0) {
>  		p9_debug(P9_DEBUG_VFS, "p9_client_open_dotl failed in 
creat %d\n",
>  			 err);
> -		p9_client_clunk(dfid);
> +		p9_fid_put(dfid);
>  		goto error;
>  	}
>  	v9fs_invalidate_inode_attr(dir);
> 
>  	/* instantiate inode and assign the unopened fid to the dentry */
>  	fid = p9_client_walk(dfid, 1, &name, 1);
> -	p9_client_clunk(dfid);
> +	p9_fid_put(dfid);
>  	if (IS_ERR(fid)) {
>  		err = PTR_ERR(fid);
>  		p9_debug(P9_DEBUG_VFS, "p9_client_walk failed %d\n", err);
> @@ -358,10 +358,10 @@ v9fs_vfs_atomic_open_dotl(struct inode *dir, struct
> dentry *dentry,
> 
>  error:
>  	if (fid)
> -		p9_client_clunk(fid);
> +		p9_fid_put(fid);
>  err_clunk_old_fid:
>  	if (ofid)
> -		p9_client_clunk(ofid);
> +		p9_fid_put(ofid);
>  	goto out;
>  }
> 
> @@ -458,9 +458,9 @@ static int v9fs_vfs_mkdir_dotl(struct user_namespace
> *mnt_userns, v9fs_invalidate_inode_attr(dir);
>  error:
>  	if (fid)
> -		p9_client_clunk(fid);
> +		p9_fid_put(fid);
>  	v9fs_put_acl(dacl, pacl);
> -	p9_client_clunk(dfid);
> +	p9_fid_put(dfid);
>  	return err;
>  }
> 
> @@ -489,7 +489,7 @@ v9fs_vfs_getattr_dotl(struct user_namespace *mnt_userns,
> */
> 
>  	st = p9_client_getattr_dotl(fid, P9_STATS_ALL);
> -	p9_client_clunk(fid);
> +	p9_fid_put(fid);
>  	if (IS_ERR(st))
>  		return PTR_ERR(st);
> 
> @@ -603,7 +603,7 @@ int v9fs_vfs_setattr_dotl(struct user_namespace
> *mnt_userns, retval = p9_client_setattr(fid, &p9attr);
>  	if (retval < 0) {
>  		if (use_dentry)
> -			p9_client_clunk(fid);
> +			p9_fid_put(fid);
>  		return retval;
>  	}
> 
> @@ -619,12 +619,12 @@ int v9fs_vfs_setattr_dotl(struct user_namespace
> *mnt_userns, retval = v9fs_acl_chmod(inode, fid);
>  		if (retval < 0) {
>  			if (use_dentry)
> -				p9_client_clunk(fid);
> +				p9_fid_put(fid);
>  			return retval;
>  		}
>  	}
>  	if (use_dentry)
> -		p9_client_clunk(fid);
> +		p9_fid_put(fid);
> 
>  	return 0;
>  }
> @@ -771,9 +771,9 @@ v9fs_vfs_symlink_dotl(struct user_namespace *mnt_userns,
> struct inode *dir,
> 
>  error:
>  	if (fid)
> -		p9_client_clunk(fid);
> +		p9_fid_put(fid);
> 
> -	p9_client_clunk(dfid);
> +	p9_fid_put(dfid);
>  	return err;
>  }
> 
> @@ -803,14 +803,14 @@ v9fs_vfs_link_dotl(struct dentry *old_dentry, struct
> inode *dir,
> 
>  	oldfid = v9fs_fid_lookup(old_dentry);
>  	if (IS_ERR(oldfid)) {
> -		p9_client_clunk(dfid);
> +		p9_fid_put(dfid);
>  		return PTR_ERR(oldfid);
>  	}
> 
>  	err = p9_client_link(dfid, oldfid, dentry->d_name.name);
> 
> -	p9_client_clunk(dfid);
> -	p9_client_clunk(oldfid);
> +	p9_fid_put(dfid);
> +	p9_fid_put(oldfid);
>  	if (err < 0) {
>  		p9_debug(P9_DEBUG_VFS, "p9_client_link failed %d\n", err);
>  		return err;
> @@ -826,7 +826,7 @@ v9fs_vfs_link_dotl(struct dentry *old_dentry, struct
> inode *dir, return PTR_ERR(fid);
> 
>  		v9fs_refresh_inode_dotl(fid, d_inode(old_dentry));
> -		p9_client_clunk(fid);
> +		p9_fid_put(fid);
>  	}
>  	ihold(d_inode(old_dentry));
>  	d_instantiate(dentry, d_inode(old_dentry));
> @@ -924,9 +924,9 @@ v9fs_vfs_mknod_dotl(struct user_namespace *mnt_userns,
> struct inode *dir, }
>  error:
>  	if (fid)
> -		p9_client_clunk(fid);
> +		p9_fid_put(fid);
>  	v9fs_put_acl(dacl, pacl);
> -	p9_client_clunk(dfid);
> +	p9_fid_put(dfid);
> 
>  	return err;
>  }
> @@ -956,7 +956,7 @@ v9fs_vfs_get_link_dotl(struct dentry *dentry,
>  	if (IS_ERR(fid))
>  		return ERR_CAST(fid);
>  	retval = p9_client_readlink(fid, &target);
> -	p9_client_clunk(fid);
> +	p9_fid_put(fid);
>  	if (retval)
>  		return ERR_PTR(retval);
>  	set_delayed_call(done, kfree_link, target);
> diff --git a/fs/9p/vfs_super.c b/fs/9p/vfs_super.c
> index 97e23b4e6982..bf350fad9500 100644
> --- a/fs/9p/vfs_super.c
> +++ b/fs/9p/vfs_super.c
> @@ -190,7 +190,7 @@ static struct dentry *v9fs_mount(struct file_system_type
> *fs_type, int flags, return dget(sb->s_root);
> 
>  clunk_fid:
> -	p9_client_clunk(fid);
> +	p9_fid_put(fid);
>  	v9fs_session_close(v9ses);
>  free_session:
>  	kfree(v9ses);
> @@ -203,7 +203,7 @@ static struct dentry *v9fs_mount(struct file_system_type
> *fs_type, int flags, * attached the fid to dentry so it won't get clunked
>  	 * automatically.
>  	 */
> -	p9_client_clunk(fid);
> +	p9_fid_put(fid);
>  	deactivate_locked_super(sb);
>  	return ERR_PTR(retval);
>  }
> @@ -270,7 +270,7 @@ static int v9fs_statfs(struct dentry *dentry, struct
> kstatfs *buf) }
>  	res = simple_statfs(dentry, buf);
>  done:
> -	p9_client_clunk(fid);
> +	p9_fid_put(fid);
>  	return res;
>  }
> 
> diff --git a/fs/9p/xattr.c b/fs/9p/xattr.c
> index a824441b95a2..1f9298a4bd42 100644
> --- a/fs/9p/xattr.c
> +++ b/fs/9p/xattr.c
> @@ -44,7 +44,7 @@ ssize_t v9fs_fid_xattr_get(struct p9_fid *fid, const char
> *name, if (err)
>  			retval = err;
>  	}
> -	p9_client_clunk(attr_fid);
> +	p9_fid_put(attr_fid);
>  	return retval;
>  }
> 
> @@ -71,7 +71,7 @@ ssize_t v9fs_xattr_get(struct dentry *dentry, const char
> *name, if (IS_ERR(fid))
>  		return PTR_ERR(fid);
>  	ret = v9fs_fid_xattr_get(fid, name, buffer, buffer_size);
> -	p9_client_clunk(fid);
> +	p9_fid_put(fid);
> 
>  	return ret;
>  }
> @@ -98,7 +98,7 @@ int v9fs_xattr_set(struct dentry *dentry, const char
> *name, if (IS_ERR(fid))
>  		return PTR_ERR(fid);
>  	ret = v9fs_fid_xattr_set(fid, name, value, value_len, flags);
> -	p9_client_clunk(fid);
> +	p9_fid_put(fid);
>  	return ret;
>  }
> 
> @@ -128,7 +128,7 @@ int v9fs_fid_xattr_set(struct p9_fid *fid, const char
> *name, retval);
>  	else
>  		p9_client_write(fid, 0, &from, &retval);
> -	err = p9_client_clunk(fid);
> +	err = p9_fid_put(fid);
>  	if (!retval && err)
>  		retval = err;
>  	return retval;
> diff --git a/include/net/9p/client.h b/include/net/9p/client.h
> index ec1d1706f43c..eabb53992350 100644
> --- a/include/net/9p/client.h
> +++ b/include/net/9p/client.h
> @@ -237,6 +237,34 @@ static inline int p9_req_try_get(struct p9_req_t *r)
> 
>  int p9_req_put(struct p9_req_t *r);
> 
> +/* fid reference counting helpers:
> + *  - fids used for any length of time should always be referenced through
> + *    p9_fid_get(), and released with p9_fid_put()
> + *  - v9fs_fid_lookup() or similar will automatically call get for you
> + *    and also require a put
> + *  - the *_fid_add() helpers will stash the fid in the inode,
> + *    at which point it is the responsibility of evict_inode()
> + *    to call the put
> + *  - the last put will automatically send a clunk to the server
> + */
> +static inline struct p9_fid *p9_fid_get(struct p9_fid *fid)
> +{
> +	refcount_inc(&fid->count);
> +
> +	return fid;
> +}
> +
> +static inline int p9_fid_put(struct p9_fid *fid)
> +{
> +	if (!fid || IS_ERR(fid))
> +		return 0;
> +
> +	if (!refcount_dec_and_test(&fid->count))
> +		return 0;
> +
> +	return p9_client_clunk(fid);
> +}
> +
>  void p9_client_cb(struct p9_client *c, struct p9_req_t *req, int status);
> 
>  int p9_parse_header(struct p9_fcall *pdu, int32_t *size, int8_t *type,
> diff --git a/net/9p/client.c b/net/9p/client.c
> index 8bba0d9cf975..f3eb280c7d9d 100644
> --- a/net/9p/client.c
> +++ b/net/9p/client.c
> @@ -1228,7 +1228,7 @@ struct p9_fid *p9_client_walk(struct p9_fid *oldfid,
> uint16_t nwname,
> 
>  clunk_fid:
>  	kfree(wqids);
> -	p9_client_clunk(fid);
> +	p9_fid_put(fid);
>  	fid = NULL;
> 
>  error:
> @@ -1459,15 +1459,6 @@ int p9_client_clunk(struct p9_fid *fid)
>  	struct p9_req_t *req;
>  	int retries = 0;
> 
> -	if (!fid || IS_ERR(fid)) {
> -		pr_warn("%s (%d): Trying to clunk with invalid fid\n",
> -			__func__, task_pid_nr(current));
> -		dump_stack();
> -		return 0;
> -	}
> -	if (!refcount_dec_and_test(&fid->count))
> -		return 0;
> -

I probably would have moved (and that way preserved) that sanity warning to 
p9_fid_put(), but anyway LGTM.

Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>

>  again:
>  	p9_debug(P9_DEBUG_9P, ">>> TCLUNK fid %d (try %d)\n",
>  		 fid->fid, retries);
> @@ -1519,7 +1510,7 @@ int p9_client_remove(struct p9_fid *fid)
>  	p9_tag_remove(clnt, req);
>  error:
>  	if (err == -ERESTARTSYS)
> -		p9_client_clunk(fid);
> +		p9_fid_put(fid);
>  	else
>  		p9_fid_destroy(fid);
>  	return err;
> @@ -2042,7 +2033,7 @@ struct p9_fid *p9_client_xattrwalk(struct p9_fid
> *file_fid, attr_fid->fid, *attr_size);
>  	return attr_fid;
>  clunk_fid:
> -	p9_client_clunk(attr_fid);
> +	p9_fid_put(attr_fid);
>  	attr_fid = NULL;
>  error:
>  	if (attr_fid && attr_fid != file_fid)