Re: [PATCH 12/27] nfsd: Push mnt_want_write() outside of i_mutex

[Jan Kara <jack@suse.cz>]

On Mon 16-04-12 14:25:33, J. Bruce Fields wrote:
> On Mon, Apr 16, 2012 at 06:13:50PM +0200, Jan Kara wrote:
> > When mnt_want_write() starts to handle freezing it will get a full lock
> > semantics requiring proper lock ordering. So push mnt_want_write() call
> > consistently outside of i_mutex.
> 
> How are you testing this?
  That's a good question :). When I wrote this, I tried running nfs server,
mounting it and checked that I could do basic operations and no lockdep
warning is emitted. If you have better idea what test I should run, I can
do that.

> And do you want this particular track merged for 3.5 through the nfsd
> tree, or should it go some other way?
  My original intent was to let Al merge everything to make it easy. But
you wish to take this patch via your tree, it should be possible (it does
not depend on anything, just the rest of the series depends on it due to
lock ordering constraints).
  
								Honza

> > CC: linux-nfs@vger.kernel.org
> > CC: "J. Bruce Fields" <bfields@fieldses.org>
> > Signed-off-by: Jan Kara <jack@suse.cz>
> > ---
> >  fs/nfsd/nfs4recover.c      |    9 +++--
> >  fs/nfsd/nfsfh.c            |    1 +
> >  fs/nfsd/nfsproc.c          |    9 ++++-
> >  fs/nfsd/vfs.c              |   79 ++++++++++++++++++++++---------------------
> >  fs/nfsd/vfs.h              |   11 +++++-
> >  include/linux/nfsd/nfsfh.h |    1 +
> >  6 files changed, 64 insertions(+), 46 deletions(-)
> > 
> > diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
> > index 4767429..efa7574 100644
> > --- a/fs/nfsd/nfs4recover.c
> > +++ b/fs/nfsd/nfs4recover.c
> > @@ -154,6 +154,10 @@ nfsd4_create_clid_dir(struct nfs4_client *clp)
> >  	if (status < 0)
> >  		return;
> >  
> > +	status = mnt_want_write_file(rec_file);
> > +	if (status)
> > +		return;
> > +
> >  	dir = rec_file->f_path.dentry;
> >  	/* lock the parent */
> >  	mutex_lock(&dir->d_inode->i_mutex);
> > @@ -173,11 +177,7 @@ nfsd4_create_clid_dir(struct nfs4_client *clp)
> >  		 * as well be forgiving and just succeed silently.
> >  		 */
> >  		goto out_put;
> > -	status = mnt_want_write_file(rec_file);
> > -	if (status)
> > -		goto out_put;
> >  	status = vfs_mkdir(dir->d_inode, dentry, S_IRWXU);
> > -	mnt_drop_write_file(rec_file);
> >  out_put:
> >  	dput(dentry);
> >  out_unlock:
> > @@ -189,6 +189,7 @@ out_unlock:
> >  				" (err %d); please check that %s exists"
> >  				" and is writeable", status,
> >  				user_recovery_dirname);
> > +	mnt_drop_write_file(rec_file);
> >  	nfs4_reset_creds(original_cred);
> >  }
> >  
> > diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
> > index 68454e7..8b93353 100644
> > --- a/fs/nfsd/nfsfh.c
> > +++ b/fs/nfsd/nfsfh.c
> > @@ -635,6 +635,7 @@ fh_put(struct svc_fh *fhp)
> >  		fhp->fh_post_saved = 0;
> >  #endif
> >  	}
> > +	fh_drop_write(fhp);
> >  	if (exp) {
> >  		cache_put(&exp->h, &svc_export_cache);
> >  		fhp->fh_export = NULL;
> > diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
> > index e15dc45..aad6d45 100644
> > --- a/fs/nfsd/nfsproc.c
> > +++ b/fs/nfsd/nfsproc.c
> > @@ -196,6 +196,7 @@ nfsd_proc_create(struct svc_rqst *rqstp, struct nfsd_createargs *argp,
> >  	struct dentry	*dchild;
> >  	int		type, mode;
> >  	__be32		nfserr;
> > +	int		hosterr;
> >  	dev_t		rdev = 0, wanted = new_decode_dev(attr->ia_size);
> >  
> >  	dprintk("nfsd: CREATE   %s %.*s\n",
> > @@ -214,6 +215,12 @@ nfsd_proc_create(struct svc_rqst *rqstp, struct nfsd_createargs *argp,
> >  	nfserr = nfserr_exist;
> >  	if (isdotent(argp->name, argp->len))
> >  		goto done;
> > +	hosterr = fh_want_write(dirfhp);
> > +	if (hosterr) {
> > +		nfserr = nfserrno(hosterr);
> > +		goto done;
> > +	}
> > +
> >  	fh_lock_nested(dirfhp, I_MUTEX_PARENT);
> >  	dchild = lookup_one_len(argp->name, dirfhp->fh_dentry, argp->len);
> >  	if (IS_ERR(dchild)) {
> > @@ -330,7 +337,7 @@ nfsd_proc_create(struct svc_rqst *rqstp, struct nfsd_createargs *argp,
> >  out_unlock:
> >  	/* We don't really need to unlock, as fh_put does it. */
> >  	fh_unlock(dirfhp);
> > -
> > +	fh_drop_write(dirfhp);
> >  done:
> >  	fh_put(dirfhp);
> >  	return nfsd_return_dirop(nfserr, resp);
> > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> > index 296d671..b8bb649 100644
> > --- a/fs/nfsd/vfs.c
> > +++ b/fs/nfsd/vfs.c
> > @@ -1276,6 +1276,10 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >  	 * If it has, the parent directory should already be locked.
> >  	 */
> >  	if (!resfhp->fh_dentry) {
> > +		host_err = fh_want_write(fhp);
> > +		if (host_err)
> > +			goto out_nfserr;
> > +
> >  		/* called from nfsd_proc_mkdir, or possibly nfsd3_proc_create */
> >  		fh_lock_nested(fhp, I_MUTEX_PARENT);
> >  		dchild = lookup_one_len(fname, dentry, flen);
> > @@ -1319,14 +1323,11 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >  		goto out;
> >  	}
> >  
> > -	host_err = fh_want_write(fhp);
> > -	if (host_err)
> > -		goto out_nfserr;
> > -
> >  	/*
> >  	 * Get the dir op function pointer.
> >  	 */
> >  	err = 0;
> > +	host_err = 0;
> >  	switch (type) {
> >  	case S_IFREG:
> >  		host_err = vfs_create(dirp, dchild, iap->ia_mode, NULL);
> > @@ -1343,10 +1344,8 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >  		host_err = vfs_mknod(dirp, dchild, iap->ia_mode, rdev);
> >  		break;
> >  	}
> > -	if (host_err < 0) {
> > -		fh_drop_write(fhp);
> > +	if (host_err < 0)
> >  		goto out_nfserr;
> > -	}
> >  
> >  	err = nfsd_create_setattr(rqstp, resfhp, iap);
> >  
> > @@ -1358,7 +1357,6 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >  	err2 = nfserrno(commit_metadata(fhp));
> >  	if (err2)
> >  		err = err2;
> > -	fh_drop_write(fhp);
> >  	/*
> >  	 * Update the file handle to get the new inode info.
> >  	 */
> > @@ -1417,6 +1415,11 @@ do_nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >  	err = nfserr_notdir;
> >  	if (!dirp->i_op->lookup)
> >  		goto out;
> > +
> > +	host_err = fh_want_write(fhp);
> > +	if (host_err)
> > +		goto out_nfserr;
> > +
> >  	fh_lock_nested(fhp, I_MUTEX_PARENT);
> >  
> >  	/*
> > @@ -1449,9 +1452,6 @@ do_nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >  		v_atime = verifier[1]&0x7fffffff;
> >  	}
> >  	
> > -	host_err = fh_want_write(fhp);
> > -	if (host_err)
> > -		goto out_nfserr;
> >  	if (dchild->d_inode) {
> >  		err = 0;
> >  
> > @@ -1522,7 +1522,6 @@ do_nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >  	if (!err)
> >  		err = nfserrno(commit_metadata(fhp));
> >  
> > -	fh_drop_write(fhp);
> >  	/*
> >  	 * Update the filehandle to get the new inode info.
> >  	 */
> > @@ -1533,6 +1532,7 @@ do_nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >  	fh_unlock(fhp);
> >  	if (dchild && !IS_ERR(dchild))
> >  		dput(dchild);
> > +	fh_drop_write(fhp);
> >   	return err;
> >   
> >   out_nfserr:
> > @@ -1613,6 +1613,11 @@ nfsd_symlink(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >  	err = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_CREATE);
> >  	if (err)
> >  		goto out;
> > +
> > +	host_err = fh_want_write(fhp);
> > +	if (host_err)
> > +		goto out_nfserr;
> > +
> >  	fh_lock(fhp);
> >  	dentry = fhp->fh_dentry;
> >  	dnew = lookup_one_len(fname, dentry, flen);
> > @@ -1620,10 +1625,6 @@ nfsd_symlink(struct svc_rqst *rqstp, struct svc_fh *fhp,
> >  	if (IS_ERR(dnew))
> >  		goto out_nfserr;
> >  
> > -	host_err = fh_want_write(fhp);
> > -	if (host_err)
> > -		goto out_nfserr;
> > -
> >  	if (unlikely(path[plen] != 0)) {
> >  		char *path_alloced = kmalloc(plen+1, GFP_KERNEL);
> >  		if (path_alloced == NULL)
> > @@ -1683,6 +1684,12 @@ nfsd_link(struct svc_rqst *rqstp, struct svc_fh *ffhp,
> >  	if (isdotent(name, len))
> >  		goto out;
> >  
> > +	host_err = fh_want_write(tfhp);
> > +	if (host_err) {
> > +		err = nfserrno(host_err);
> > +		goto out;
> > +	}
> > +
> >  	fh_lock_nested(ffhp, I_MUTEX_PARENT);
> >  	ddir = ffhp->fh_dentry;
> >  	dirp = ddir->d_inode;
> > @@ -1694,18 +1701,13 @@ nfsd_link(struct svc_rqst *rqstp, struct svc_fh *ffhp,
> >  
> >  	dold = tfhp->fh_dentry;
> >  
> > -	host_err = fh_want_write(tfhp);
> > -	if (host_err) {
> > -		err = nfserrno(host_err);
> > -		goto out_dput;
> > -	}
> >  	err = nfserr_noent;
> >  	if (!dold->d_inode)
> > -		goto out_drop_write;
> > +		goto out_dput;
> >  	host_err = nfsd_break_lease(dold->d_inode);
> >  	if (host_err) {
> >  		err = nfserrno(host_err);
> > -		goto out_drop_write;
> > +		goto out_dput;
> >  	}
> >  	host_err = vfs_link(dold, dirp, dnew);
> >  	if (!host_err) {
> > @@ -1718,12 +1720,11 @@ nfsd_link(struct svc_rqst *rqstp, struct svc_fh *ffhp,
> >  		else
> >  			err = nfserrno(host_err);
> >  	}
> > -out_drop_write:
> > -	fh_drop_write(tfhp);
> >  out_dput:
> >  	dput(dnew);
> >  out_unlock:
> >  	fh_unlock(ffhp);
> > +	fh_drop_write(tfhp);
> >  out:
> >  	return err;
> >  
> > @@ -1766,6 +1767,12 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
> >  	if (!flen || isdotent(fname, flen) || !tlen || isdotent(tname, tlen))
> >  		goto out;
> >  
> > +	host_err = fh_want_write(ffhp);
> > +	if (host_err) {
> > +		err = nfserrno(host_err);
> > +		goto out;
> > +	}
> > +
> >  	/* cannot use fh_lock as we need deadlock protective ordering
> >  	 * so do it by hand */
> >  	trap = lock_rename(tdentry, fdentry);
> > @@ -1796,17 +1803,14 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
> >  	host_err = -EXDEV;
> >  	if (ffhp->fh_export->ex_path.mnt != tfhp->fh_export->ex_path.mnt)
> >  		goto out_dput_new;
> > -	host_err = fh_want_write(ffhp);
> > -	if (host_err)
> > -		goto out_dput_new;
> >  
> >  	host_err = nfsd_break_lease(odentry->d_inode);
> >  	if (host_err)
> > -		goto out_drop_write;
> > +		goto out_dput_new;
> >  	if (ndentry->d_inode) {
> >  		host_err = nfsd_break_lease(ndentry->d_inode);
> >  		if (host_err)
> > -			goto out_drop_write;
> > +			goto out_dput_new;
> >  	}
> >  	host_err = vfs_rename(fdir, odentry, tdir, ndentry);
> >  	if (!host_err) {
> > @@ -1814,8 +1818,6 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
> >  		if (!host_err)
> >  			host_err = commit_metadata(ffhp);
> >  	}
> > -out_drop_write:
> > -	fh_drop_write(ffhp);
> >   out_dput_new:
> >  	dput(ndentry);
> >   out_dput_old:
> > @@ -1831,6 +1833,7 @@ out_drop_write:
> >  	fill_post_wcc(tfhp);
> >  	unlock_rename(tdentry, fdentry);
> >  	ffhp->fh_locked = tfhp->fh_locked = 0;
> > +	fh_drop_write(ffhp);
> >  
> >  out:
> >  	return err;
> > @@ -1856,6 +1859,10 @@ nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
> >  	if (err)
> >  		goto out;
> >  
> > +	host_err = fh_want_write(fhp);
> > +	if (host_err)
> > +		goto out_nfserr;
> > +
> >  	fh_lock_nested(fhp, I_MUTEX_PARENT);
> >  	dentry = fhp->fh_dentry;
> >  	dirp = dentry->d_inode;
> > @@ -1874,21 +1881,15 @@ nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
> >  	if (!type)
> >  		type = rdentry->d_inode->i_mode & S_IFMT;
> >  
> > -	host_err = fh_want_write(fhp);
> > -	if (host_err)
> > -		goto out_put;
> > -
> >  	host_err = nfsd_break_lease(rdentry->d_inode);
> >  	if (host_err)
> > -		goto out_drop_write;
> > +		goto out_put;
> >  	if (type != S_IFDIR)
> >  		host_err = vfs_unlink(dirp, rdentry);
> >  	else
> >  		host_err = vfs_rmdir(dirp, rdentry);
> >  	if (!host_err)
> >  		host_err = commit_metadata(fhp);
> > -out_drop_write:
> > -	fh_drop_write(fhp);
> >  out_put:
> >  	dput(rdentry);
> >  
> > diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
> > index ec0611b..359594c 100644
> > --- a/fs/nfsd/vfs.h
> > +++ b/fs/nfsd/vfs.h
> > @@ -110,12 +110,19 @@ int nfsd_set_posix_acl(struct svc_fh *, int, struct posix_acl *);
> >  
> >  static inline int fh_want_write(struct svc_fh *fh)
> >  {
> > -	return mnt_want_write(fh->fh_export->ex_path.mnt);
> > +	int ret = mnt_want_write(fh->fh_export->ex_path.mnt);
> > +
> > +	if (!ret)
> > +		fh->fh_want_write = 1;
> > +	return ret;
> >  }
> >  
> >  static inline void fh_drop_write(struct svc_fh *fh)
> >  {
> > -	mnt_drop_write(fh->fh_export->ex_path.mnt);
> > +	if (fh->fh_want_write) {
> > +		fh->fh_want_write = 0;
> > +		mnt_drop_write(fh->fh_export->ex_path.mnt);
> > +	}
> >  }
> >  
> >  #endif /* LINUX_NFSD_VFS_H */
> > diff --git a/include/linux/nfsd/nfsfh.h b/include/linux/nfsd/nfsfh.h
> > index ce4743a..fa63048 100644
> > --- a/include/linux/nfsd/nfsfh.h
> > +++ b/include/linux/nfsd/nfsfh.h
> > @@ -143,6 +143,7 @@ typedef struct svc_fh {
> >  	int			fh_maxsize;	/* max size for fh_handle */
> >  
> >  	unsigned char		fh_locked;	/* inode locked by us */
> > +	unsigned char		fh_want_write;	/* remount protection taken */
> >  
> >  #ifdef CONFIG_NFSD_V3
> >  	unsigned char		fh_post_saved;	/* post-op attrs saved */
> > -- 
> > 1.7.1
> > 
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR