NFS: Ensure that we free the rpc_task after read and write cleanups are done

This patch ensures that we free the rpc_task after the cleanup callbacks
are done in order to avoid a deadlock problem that can be triggered if
the callback needs to wait for another workqueue item to complete.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Weston Andros Adamson <dros@netapp.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Bruce Fields <bfields@fieldses.org>
Cc: stable@vger.kernel.org [>= 3.5]

1 files changed, 7 insertions, 3 deletions

diff --git a/fs/nfs/read.c b/fs/nfs/read.c
index b6bdb18e892c..a5e5d9899d56 100644
--- a/fs/nfs/read.c
+++ b/fs/nfs/read.c
@@ -91,12 +91,16 @@ void nfs_readdata_release(struct nfs_read_data *rdata)
         put_nfs_open_context(rdata->args.context);
         if (rdata->pages.pagevec != rdata->pages.page_array)
                 kfree(rdata->pages.pagevec);
-        if (rdata != &read_header->rpc_data)
-                kfree(rdata);
-        else
+        if (rdata == &read_header->rpc_data) {
                 rdata->header = NULL;
+                rdata = NULL;
+        }
         if (atomic_dec_and_test(&hdr->refcnt))
                 hdr->completion_ops->completion(hdr);
+        /* Note: we only free the rpc_task after callbacks are done.
+         * See the comment in rpc_free_task() for why
+         */
+        kfree(rdata);
 }
 EXPORT_SYMBOL_GPL(nfs_readdata_release);