teach nfs_get_link() to work in RCU mode

based upon the corresponding patch from Neil's March patchset,
again with kmap-related horrors removed.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 42 insertions, 10 deletions

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index ae9aa0b8155c..aa828e8b6e04 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -1087,6 +1087,27 @@ static bool nfs_mapping_need_revalidate_inode(struct inode *inode)
                 || NFS_STALE(inode);
 }
 
+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;
+}
+
 /**
  * __nfs_revalidate_mapping - Revalidate the pagecache
  * @inode - pointer to host inode
diff --git a/fs/nfs/symlink.c b/fs/nfs/symlink.c
index 8ade8a812607..95c69af7e4d0 100644
--- a/fs/nfs/symlink.c
+++ b/fs/nfs/symlink.c
@@ -48,16 +48,26 @@ static const char *nfs_get_link(struct dentry *dentry,
         struct page *page;
         void *err;
 
-        if (!dentry)
-                return ERR_PTR(-ECHILD);
-
-        err = ERR_PTR(nfs_revalidate_mapping(inode, inode->i_mapping));
-        if (err)
-                return err;
-        page = read_cache_page(&inode->i_data, 0,
-                                (filler_t *)nfs_symlink_filler, inode);
-        if (IS_ERR(page))
-                return ERR_CAST(page);
+        if (!dentry) {
+                err = ERR_PTR(nfs_revalidate_mapping_rcu(inode));
+                if (err)
+                        return err;
+                page = find_get_page(inode->i_mapping, 0);
+                if (!page)
+                        return ERR_PTR(-ECHILD);
+                if (!PageUptodate(page)) {
+                        put_page(page);
+                        return ERR_PTR(-ECHILD);
+                }
+        } else {
+                err = ERR_PTR(nfs_revalidate_mapping(inode, inode->i_mapping));
+                if (err)
+                        return err;
+                page = read_cache_page(&inode->i_data, 0,
+                                        (filler_t *)nfs_symlink_filler, inode);
+                if (IS_ERR(page))
+                        return ERR_CAST(page);
+        }
         *cookie = page;
         return page_address(page);
 }
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index c0e961474a52..37a3d2981352 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -359,6 +359,7 @@ extern int nfs_revalidate_inode(struct nfs_server *server, struct inode *inode);
 extern int nfs_revalidate_inode_rcu(struct nfs_server *server, struct inode *inode);
 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_rcu(struct inode *inode);
 extern int nfs_revalidate_mapping_protected(struct inode *inode, struct address_space *mapping);
 extern int nfs_setattr(struct dentry *, struct iattr *);
 extern void nfs_setattr_update_inode(struct inode *inode, struct iattr *attr, struct nfs_fattr *);