fs/9p: Fix race in initializing writeback fid

When two process open the same file we can end up with both of them
allocating the writeback_fid. Add a new mutex which can be used
for synchronizing v9fs_inode member values.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
index 78bcb97c3425..3337d58d0fc5 100644
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -90,6 +90,7 @@ int v9fs_file_open(struct inode *inode, struct file *file)
         }
 
         file->private_data = fid;
+        mutex_lock(&v9inode->v_mutex);
         if (v9ses->cache && !v9inode->writeback_fid) {
                 /*
                  * clone a fid and add it to writeback_fid
@@ -101,10 +102,12 @@ int v9fs_file_open(struct inode *inode, struct file *file)
                 fid = v9fs_writeback_fid(file->f_path.dentry);
                 if (IS_ERR(fid)) {
                         err = PTR_ERR(fid);
+                        mutex_unlock(&v9inode->v_mutex);
                         goto out_error;
                 }
                 v9inode->writeback_fid = (void *) fid;
         }
+        mutex_unlock(&v9inode->v_mutex);
 #ifdef CONFIG_9P_FSCACHE
         if (v9ses->cache)
                 v9fs_cache_inode_set_cookie(inode, file);