NFS: Fix a race with PG_private and nfs_release_page()

We don't need to set PG_private for readahead pages, since they never get
unlocked while I/O is in progress. However there is a small race in
nfs_readpage_release() whereby the page may be unlocked, and have
PG_private set.

Fix is to have PG_private set only for the case of writes...

Also fix a bug in nfs_clear_page_writeback(): Don't attempt to clear the
radix_tree tag if we've already deleted the radix tree entry.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 7 insertions, 5 deletions

diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index d6e076c9dbe1..106aca388ebc 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -88,7 +88,6 @@ nfs_create_request(struct nfs_open_context *ctx, struct inode *inode,
         BUG_ON(PagePrivate(page));
         BUG_ON(!PageLocked(page));
         BUG_ON(page->mapping->host != inode);
-        SetPagePrivate(page);
         req->wb_offset  = offset;
         req->wb_pgbase  = offset;
         req->wb_bytes   = count;
@@ -136,9 +135,11 @@ void nfs_clear_page_writeback(struct nfs_page *req)
 {
         struct nfs_inode *nfsi = NFS_I(req->wb_context->dentry->d_inode);
 
-        spin_lock(&nfsi->req_lock);
-        radix_tree_tag_clear(&nfsi->nfs_page_tree, req->wb_index, NFS_PAGE_TAG_WRITEBACK);
-        spin_unlock(&nfsi->req_lock);
+        if (req->wb_page != NULL) {
+                spin_lock(&nfsi->req_lock);
+                radix_tree_tag_clear(&nfsi->nfs_page_tree, req->wb_index, NFS_PAGE_TAG_WRITEBACK);
+                spin_unlock(&nfsi->req_lock);
+        }
         nfs_unlock_request(req);
 }
 
@@ -153,7 +154,6 @@ void nfs_clear_request(struct nfs_page *req)
 {
         struct page *page = req->wb_page;
         if (page != NULL) {
-                ClearPagePrivate(page);
                 page_cache_release(page);
                 req->wb_page = NULL;
         }
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 647e3217c2e1..d9e5ee594572 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -429,6 +429,7 @@ static int nfs_inode_add_request(struct inode *inode, struct nfs_page *req)
                 if (nfs_have_delegation(inode, FMODE_WRITE))
                         nfsi->change_attr++;
         }
+        SetPagePrivate(req->wb_page);
         nfsi->npages++;
         atomic_inc(&req->wb_count);
         return 0;
@@ -445,6 +446,7 @@ static void nfs_inode_remove_request(struct nfs_page *req)
         BUG_ON (!NFS_WBACK_BUSY(req));
 
         spin_lock(&nfsi->req_lock);
+        ClearPagePrivate(req->wb_page);
         radix_tree_delete(&nfsi->nfs_page_tree, req->wb_index);
         nfsi->npages--;
         if (!nfsi->npages) {