Commit d51ac1a8 authored by NeilBrown's avatar NeilBrown Committed by Trond Myklebust
Browse files

NFS: prepare for RCU-walk support but pushing tests later in code. 



nfs_lookup_revalidate, nfs4_lookup_revalidate, and nfs_permission
all need to understand and handle RCU-walk for NFS to gain the
benefits of RCU-walk for cached information.

Currently these functions all immediately return -ECHILD
if the relevant flag (LOOKUP_RCU or MAY_NOT_BLOCK) is set.

This patch pushes those tests later in the code so that we only abort
immediately before we enter rcu-unsafe code.  As subsequent patches
make that rcu-unsafe code rcu-safe, several of these new tests will
disappear.

With this patch there are several paths through the code which will no
longer return -ECHILD during an RCU-walk.  However these are mostly
error paths or other uninteresting cases.

A noteworthy change in nfs_lookup_revalidate is that we don't take
(or put) the reference to ->d_parent when LOOKUP_RCU is set.
Rather we rcu_dereference ->d_parent, and check that ->d_inode
is not NULL.  We also check that ->d_parent hasn't changed after
all the tests.

In nfs4_lookup_revalidate we simply avoid testing LOOKUP_RCU on the
path that only calls nfs_lookup_revalidate() as that function
already performs the required test.

Signed-off-by: default avatarNeilBrown <neilb@suse.de>
Signed-off-by: default avatarTrond Myklebust <trond.myklebust@primarydata.com>
parent 49317a7f

fs/nfs/dir.c

+33 −12
Original line number Diff line number Diff line
@@ -1088,21 +1088,30 @@ static int nfs_lookup_revalidate(struct dentry *dentry, unsigned int flags) 
	struct nfs4_label *label = NULL;

	int error;



	if (flags & LOOKUP_RCU)

	if (flags & LOOKUP_RCU) {

		parent = rcu_dereference(dentry->d_parent);

		dir = ACCESS_ONCE(parent->d_inode);

		if (!dir)

			return -ECHILD;



	} else {

		parent = dget_parent(dentry);

		dir = parent->d_inode;

	}

	nfs_inc_stats(dir, NFSIOS_DENTRYREVALIDATE);

	inode = dentry->d_inode;



	if (!inode) {

		if (flags & LOOKUP_RCU)

			return -ECHILD;



		if (nfs_neg_need_reval(dir, dentry, flags))

			goto out_bad;

		goto out_valid_noent;

	}



	if (is_bad_inode(inode)) {

		if (flags & LOOKUP_RCU)

			return -ECHILD;

		dfprintk(LOOKUPCACHE, "%s: %pd2 has dud inode\n",

				__func__, dentry);

		goto out_bad;
@@ -1111,6 +1120,9 @@ static int nfs_lookup_revalidate(struct dentry *dentry, unsigned int flags) 
	if (NFS_PROTO(dir)->have_delegation(inode, FMODE_READ))

		goto out_set_verifier;



	if (flags & LOOKUP_RCU)

		return -ECHILD;



	/* Force a full look up iff the parent directory has changed */

	if (!nfs_is_exclusive_create(dir, flags) && nfs_check_verifier(dir, dentry)) {

		if (nfs_lookup_verify_inode(inode, flags))
@@ -1153,6 +1165,10 @@ out_set_verifier: 
	/* Success: notify readdir to use READDIRPLUS */

	nfs_advise_use_readdirplus(dir);

 out_valid_noent:

	if (flags & LOOKUP_RCU) {

		if (parent != rcu_dereference(dentry->d_parent))

			return -ECHILD;

	} else

		dput(parent);

	dfprintk(LOOKUPCACHE, "NFS: %s(%pd2) is valid\n",

			__func__, dentry);
@@ -1160,6 +1176,7 @@ out_set_verifier: 
out_zap_parent:

	nfs_zap_caches(dir);

 out_bad:

	WARN_ON(flags & LOOKUP_RCU);

	nfs_free_fattr(fattr);

	nfs_free_fhandle(fhandle);

	nfs4_label_free(label);
@@ -1185,6 +1202,7 @@ out_zap_parent: 
			__func__, dentry);

	return 0;

out_error:

	WARN_ON(flags & LOOKUP_RCU);

	nfs_free_fattr(fattr);

	nfs_free_fhandle(fhandle);

	nfs4_label_free(label);
@@ -1532,9 +1550,6 @@ static int nfs4_lookup_revalidate(struct dentry *dentry, unsigned int flags) 
	struct inode *inode;

	int ret = 0;



	if (flags & LOOKUP_RCU)

		return -ECHILD;



	if (!(flags & LOOKUP_OPEN) || (flags & LOOKUP_DIRECTORY))

		goto no_open;

	if (d_mountpoint(dentry))
@@ -1551,6 +1566,9 @@ static int nfs4_lookup_revalidate(struct dentry *dentry, unsigned int flags) 
		struct dentry *parent;

		struct inode *dir;



		if (flags & LOOKUP_RCU)

			return -ECHILD;



		parent = dget_parent(dentry);

		dir = parent->d_inode;

		if (!nfs_neg_need_reval(dir, dentry, flags))
@@ -2348,9 +2366,6 @@ int nfs_permission(struct inode *inode, int mask) 
	struct rpc_cred *cred;

	int res = 0;



	if (mask & MAY_NOT_BLOCK)

		return -ECHILD;



	nfs_inc_stats(inode, NFSIOS_VFSACCESS);



	if ((mask & (MAY_READ | MAY_WRITE | MAY_EXEC)) == 0)
@@ -2377,6 +2392,9 @@ force_lookup: 
	if (!NFS_PROTO(inode)->access)

		goto out_notsup;



	if (mask & MAY_NOT_BLOCK)

		return -ECHILD;



	cred = rpc_lookup_cred();

	if (!IS_ERR(cred)) {

		res = nfs_do_access(inode, cred, mask);
@@ -2391,6 +2409,9 @@ out: 
		inode->i_sb->s_id, inode->i_ino, mask, res);

	return res;

out_notsup:

	if (mask & MAY_NOT_BLOCK)

		return -ECHILD;



	res = nfs_revalidate_inode(NFS_SERVER(inode), inode);

	if (res == 0)

		res = generic_permission(inode, mask);

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