[PATCH 20/20] NFS: support LOOKUP_RCU in nfs_follow_link.

[NeilBrown <neilb@xxxxxxx>]

If the inode is valid and the page has been read in,
then we can follow a link in RCU-walk.

Signed-off-by: NeilBrown <neilb@xxxxxxx>
---
 fs/nfs/inode.c         |   21 +++++++++++++++++++++
 fs/nfs/symlink.c       |   20 ++++++++++++++++++--
 include/linux/nfs_fs.h |    1 +
 3 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index d42dff6d5e98..430899a789c6 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -1162,6 +1162,27 @@ int nfs_revalidate_mapping_protected(struct inode *inode, struct address_space *
 	return __nfs_revalidate_mapping(inode, mapping, true);
 }
 
+int nfs_revalidate_mapping_rcu(struct inode *inode)
+{
+	struct nfs_inode *nfsi = NFS_I(inode);
+	unsigned long *bitlock = &nfsi->flags;
+	int ret = 0;
+
+	if (IS_SWAPFILE(inode))
+		goto out;
+	if (nfs_mapping_need_revalidate_inode(inode)) {
+		ret = -ECHILD;
+		goto out;
+	}
+	spin_lock(&inode->i_lock);
+	if (test_bit(NFS_INO_INVALIDATING, bitlock) ||
+	    (nfsi->cache_validity & NFS_INO_INVALID_DATA))
+		ret = -ECHILD;
+	spin_unlock(&inode->i_lock);
+out:
+	return ret;
+}
+
 static unsigned long nfs_wcc_update_inode(struct inode *inode, struct nfs_fattr *fattr)
 {
 	struct nfs_inode *nfsi = NFS_I(inode);
diff --git a/fs/nfs/symlink.c b/fs/nfs/symlink.c
index 32bbac1bb4bc..1c0a94b3d12e 100644
--- a/fs/nfs/symlink.c
+++ b/fs/nfs/symlink.c
@@ -49,8 +49,24 @@ static void *nfs_follow_link(struct dentry *dentry, struct inode *inode,
 	struct page *page;
 	void *err;
 
-	if (flags & LOOKUP_RCU)
-		return ERR_PTR(-ECHILD);
+	if (flags & LOOKUP_RCU) {
+		err = ERR_PTR(nfs_revalidate_mapping_rcu(inode));
+		if (err)
+			goto read_failed;
+		page = find_get_page(inode->i_mapping, 0);
+		if (page &&
+		    (!PageUptodate(page) || PageHighMem(page))) {
+			put_page(page);
+			page = NULL;
+		}
+		if (!page) {
+			err = ERR_PTR(-ECHILD);
+			goto read_failed;
+		}
+		nd_set_link(page_address(page));
+		page = (void *)((unsigned long)page | 1);
+		return page;
+	}
 	err = ERR_PTR(nfs_revalidate_mapping(inode, inode->i_mapping));
 	if (err)
 		goto read_failed;
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index b01ccf371fdc..2eea59456ebb 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -357,6 +357,7 @@ extern int nfs_revalidate_inode_rcu(struct nfs_server *server, struct inode *ino
 extern int __nfs_revalidate_inode(struct nfs_server *, struct inode *);
 extern int nfs_revalidate_mapping(struct inode *inode, struct address_space *mapping);
 extern int nfs_revalidate_mapping_protected(struct inode *inode, struct address_space *mapping);
+extern int nfs_revalidate_mapping_rcu(struct inode *inode);
 extern int nfs_setattr(struct dentry *, struct iattr *);
 extern void nfs_setattr_update_inode(struct inode *inode, struct iattr *attr, struct nfs_fattr *);
 extern void nfs_setsecurity(struct inode *inode, struct nfs_fattr *fattr,


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