NFS: Fix a hang in the writeback path

Now that the inode scalability patches have been merged, it is no longer
safe to call igrab() under the inode->i_lock.
Now that we no longer call nfs_clear_request() until the nfs_page is
being freed, we know that we are always holding a reference to the
nfs_open_context, which again holds a reference to the path, and so
the inode cannot be freed until the last nfs_page has been removed
from the radix tree and freed.

We can therefore skip the igrab()/iput() altogether.

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

2 files changed, 5 insertions, 12 deletions

diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index 87a593c2b055..c80add6e2213 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -135,14 +135,14 @@ void nfs_clear_page_tag_locked(struct nfs_page *req)
                 nfs_unlock_request(req);
 }
 
-/**
+/*
  * nfs_clear_request - Free up all resources allocated to the request
  * @req:
  *
  * Release page and open context resources associated with a read/write
  * request after it has completed.
  */
-void nfs_clear_request(struct nfs_page *req)
+static void nfs_clear_request(struct nfs_page *req)
 {
         struct page *page = req->wb_page;
         struct nfs_open_context *ctx = req->wb_context;
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 85d75254328e..af0c6279a4a7 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -389,11 +389,8 @@ static int nfs_inode_add_request(struct inode *inode, struct nfs_page *req)
         spin_lock(&inode->i_lock);
         error = radix_tree_insert(&nfsi->nfs_page_tree, req->wb_index, req);
         BUG_ON(error);
-        if (!nfsi->npages) {
-                igrab(inode);
-                if (nfs_have_delegation(inode, FMODE_WRITE))
-                        nfsi->change_attr++;
-        }
+        if (!nfsi->npages && nfs_have_delegation(inode, FMODE_WRITE))
+                nfsi->change_attr++;
         set_bit(PG_MAPPED, &req->wb_flags);
         SetPagePrivate(req->wb_page);
         set_page_private(req->wb_page, (unsigned long)req);
@@ -423,11 +420,7 @@ static void nfs_inode_remove_request(struct nfs_page *req)
         clear_bit(PG_MAPPED, &req->wb_flags);
         radix_tree_delete(&nfsi->nfs_page_tree, req->wb_index);
         nfsi->npages--;
-        if (!nfsi->npages) {
-                spin_unlock(&inode->i_lock);
-                iput(inode);
-        } else
-                spin_unlock(&inode->i_lock);
+        spin_unlock(&inode->i_lock);
         nfs_release_request(req);
 }