Re: [PATCH v3 01/10] xattr: break delegations in {set,remove}xattr

[Frank van der Linden <fllinden@amazon.com>]

On Thu, Jun 25, 2020 at 08:39:54PM +0000, Frank van der Linden wrote:
> Hi Al,
> 
> Do you have any comments / concerns about this patch? It's part of nfs
> server side user xattr support, full series here:
> 
> https://lore.kernel.org/linux-nfs/20200623223927.31795-1-fllinden@amazon.com/
> 
> I copied this one to linux-fsdevel and you, just giving you an extra
> ping. Bruce/Chuck are OK with the rest of the series, so I just need
> your ACK on this one, and the next one (will send the ping separately).
> 
> Thanks,
> 
> - Frank

Hi Al,

Any comments on this one?

It's a simple change to break (NFSv4) delegations on set/removexattr, so it's pretty nfsd specific.

Linus - since this is nfsd specific, could this go in through the nfsd maintainer tree directly? Chuck has included it in a tree that is being readied for 5.9.

Thanks,

- Frank
> 
> 
> On Tue, Jun 23, 2020 at 10:39:18PM +0000, Frank van der Linden wrote:
> > set/removexattr on an exported filesystem should break NFS delegations.
> > This is true in general, but also for the upcoming support for
> > RFC 8726 (NFSv4 extended attribute support). Make sure that they do.
> > 
> > Additonally, they need to grow a _locked variant, since callers might
> > call this with i_rwsem held (like the NFS server code).
> > 
> > Cc: stable@vger.kernel.org
> > Cc: linux-fsdevel@vger.kernel.org
> > Cc: Al Viro <viro@zeniv.linux.org.uk>
> > Signed-off-by: Frank van der Linden <fllinden@amazon.com>
> > ---
> >  fs/xattr.c            | 84 +++++++++++++++++++++++++++++++++++++++----
> >  include/linux/xattr.h |  2 ++
> >  2 files changed, 79 insertions(+), 7 deletions(-)
> > 
> > diff --git a/fs/xattr.c b/fs/xattr.c
> > index 91608d9bfc6a..95f38f57347f 100644
> > --- a/fs/xattr.c
> > +++ b/fs/xattr.c
> > @@ -204,10 +204,22 @@ int __vfs_setxattr_noperm(struct dentry *dentry, const char *name,
> >  	return error;
> >  }
> >  
> > -
> > +/**
> > + * __vfs_setxattr_locked: set an extended attribute while holding the inode
> > + * lock
> > + *
> > + *  @dentry - object to perform setxattr on
> > + *  @name - xattr name to set
> > + *  @value - value to set @name to
> > + *  @size - size of @value
> > + *  @flags - flags to pass into filesystem operations
> > + *  @delegated_inode - on return, will contain an inode pointer that
> > + *  a delegation was broken on, NULL if none.
> > + */
> >  int
> > -vfs_setxattr(struct dentry *dentry, const char *name, const void *value,
> > -		size_t size, int flags)
> > +__vfs_setxattr_locked(struct dentry *dentry, const char *name,
> > +		const void *value, size_t size, int flags,
> > +		struct inode **delegated_inode)
> >  {
> >  	struct inode *inode = dentry->d_inode;
> >  	int error;
> > @@ -216,15 +228,40 @@ vfs_setxattr(struct dentry *dentry, const char *name, const void *value,
> >  	if (error)
> >  		return error;
> >  
> > -	inode_lock(inode);
> >  	error = security_inode_setxattr(dentry, name, value, size, flags);
> >  	if (error)
> >  		goto out;
> >  
> > +	error = try_break_deleg(inode, delegated_inode);
> > +	if (error)
> > +		goto out;
> > +
> >  	error = __vfs_setxattr_noperm(dentry, name, value, size, flags);
> >  
> >  out:
> > +	return error;
> > +}
> > +EXPORT_SYMBOL_GPL(__vfs_setxattr_locked);
> > +
> > +int
> > +vfs_setxattr(struct dentry *dentry, const char *name, const void *value,
> > +		size_t size, int flags)
> > +{
> > +	struct inode *inode = dentry->d_inode;
> > +	struct inode *delegated_inode = NULL;
> > +	int error;
> > +
> > +retry_deleg:
> > +	inode_lock(inode);
> > +	error = __vfs_setxattr_locked(dentry, name, value, size, flags,
> > +	    &delegated_inode);
> >  	inode_unlock(inode);
> > +
> > +	if (delegated_inode) {
> > +		error = break_deleg_wait(&delegated_inode);
> > +		if (!error)
> > +			goto retry_deleg;
> > +	}
> >  	return error;
> >  }
> >  EXPORT_SYMBOL_GPL(vfs_setxattr);
> > @@ -378,8 +415,18 @@ __vfs_removexattr(struct dentry *dentry, const char *name)
> >  }
> >  EXPORT_SYMBOL(__vfs_removexattr);
> >  
> > +/**
> > + * __vfs_removexattr_locked: set an extended attribute while holding the inode
> > + * lock
> > + *
> > + *  @dentry - object to perform setxattr on
> > + *  @name - name of xattr to remove
> > + *  @delegated_inode - on return, will contain an inode pointer that
> > + *  a delegation was broken on, NULL if none.
> > + */
> >  int
> > -vfs_removexattr(struct dentry *dentry, const char *name)
> > +__vfs_removexattr_locked(struct dentry *dentry, const char *name,
> > +		struct inode **delegated_inode)
> >  {
> >  	struct inode *inode = dentry->d_inode;
> >  	int error;
> > @@ -388,11 +435,14 @@ vfs_removexattr(struct dentry *dentry, const char *name)
> >  	if (error)
> >  		return error;
> >  
> > -	inode_lock(inode);
> >  	error = security_inode_removexattr(dentry, name);
> >  	if (error)
> >  		goto out;
> >  
> > +	error = try_break_deleg(inode, delegated_inode);
> > +	if (error)
> > +		goto out;
> > +
> >  	error = __vfs_removexattr(dentry, name);
> >  
> >  	if (!error) {
> > @@ -401,12 +451,32 @@ vfs_removexattr(struct dentry *dentry, const char *name)
> >  	}
> >  
> >  out:
> > +	return error;
> > +}
> > +EXPORT_SYMBOL_GPL(__vfs_removexattr_locked);
> > +
> > +int
> > +vfs_removexattr(struct dentry *dentry, const char *name)
> > +{
> > +	struct inode *inode = dentry->d_inode;
> > +	struct inode *delegated_inode = NULL;
> > +	int error;
> > +
> > +retry_deleg:
> > +	inode_lock(inode);
> > +	error = __vfs_removexattr_locked(dentry, name, &delegated_inode);
> >  	inode_unlock(inode);
> > +
> > +	if (delegated_inode) {
> > +		error = break_deleg_wait(&delegated_inode);
> > +		if (!error)
> > +			goto retry_deleg;
> > +	}
> > +
> >  	return error;
> >  }
> >  EXPORT_SYMBOL_GPL(vfs_removexattr);
> >  
> > -
> >  /*
> >   * Extended attribute SET operations
> >   */
> > diff --git a/include/linux/xattr.h b/include/linux/xattr.h
> > index 47eaa34f8761..a2f3cd02653c 100644
> > --- a/include/linux/xattr.h
> > +++ b/include/linux/xattr.h
> > @@ -51,8 +51,10 @@ ssize_t vfs_getxattr(struct dentry *, const char *, void *, size_t);
> >  ssize_t vfs_listxattr(struct dentry *d, char *list, size_t size);
> >  int __vfs_setxattr(struct dentry *, struct inode *, const char *, const void *, size_t, int);
> >  int __vfs_setxattr_noperm(struct dentry *, const char *, const void *, size_t, int);
> > +int __vfs_setxattr_locked(struct dentry *, const char *, const void *, size_t, int, struct inode **);
> >  int vfs_setxattr(struct dentry *, const char *, const void *, size_t, int);
> >  int __vfs_removexattr(struct dentry *, const char *);
> > +int __vfs_removexattr_locked(struct dentry *, const char *, struct inode **);
> >  int vfs_removexattr(struct dentry *, const char *);
> >  
> >  ssize_t generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size);
> > -- 
> > 2.17.2
> >