NFS: Fix a deadlock with lazy umount

We can't allow rpc callback functions like task->tk_ops->rpc_call_prepare()
and task->tk_ops->rpc_call_done() to call mntput() in any way, since
that will cause a deadlock when the call to rpc_shutdown_client() attempts
to wait on 'task' to complete.

We can avoid the above deadlock by moving calls to mntput to
task->tk_ops->rpc_release() callback, since at that time the task will be
marked as completed, and so rpc_shutdown_client won't attempt to wait on
it.

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

1 files changed, 10 insertions, 3 deletions

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 80c61fdb2720..69b4158d9a10 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -105,8 +105,11 @@ static void nfs_writedata_free(struct nfs_write_data *wdata)
         call_rcu_bh(&wdata->task.u.tk_rcu, nfs_writedata_rcu_free);
 }
 
-void nfs_writedata_release(void *wdata)
+void nfs_writedata_release(void *data)
 {
+        struct nfs_write_data *wdata = data;
+
+        put_nfs_open_context(wdata->args.context);
         nfs_writedata_free(wdata);
 }
 
@@ -816,7 +819,7 @@ static void nfs_write_rpcsetup(struct nfs_page *req,
         data->args.pgbase = req->wb_pgbase + offset;
         data->args.pages  = data->pagevec;
         data->args.count  = count;
-        data->args.context = req->wb_context;
+        data->args.context = get_nfs_open_context(req->wb_context);
         data->args.stable  = NFS_UNSTABLE;
         if (how & FLUSH_STABLE) {
                 data->args.stable = NFS_DATA_SYNC;
@@ -1153,8 +1156,11 @@ int nfs_writeback_done(struct rpc_task *task, struct nfs_write_data *data)
 
 
 #if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
-void nfs_commit_release(void *wdata)
+void nfs_commit_release(void *data)
 {
+        struct nfs_write_data *wdata = data;
+
+        put_nfs_open_context(wdata->args.context);
         nfs_commit_free(wdata);
 }
 
@@ -1197,6 +1203,7 @@ static void nfs_commit_rpcsetup(struct list_head *head,
         /* Note: we always request a commit of the entire inode */
         data->args.offset = 0;
         data->args.count  = 0;
+        data->args.context = get_nfs_open_context(first->wb_context);
         data->res.count   = 0;
         data->res.fattr   = &data->fattr;
         data->res.verf    = &data->verf;