CIFS: keep FileInfo handle live during oplock break

In the oplock break handler, writing pending changes from pages puts
the FileInfo handle. If the refcount reaches zero it closes the handle
and waits for any oplock break handler to return, thus causing a deadlock.

To prevent this situation:

* We add a wait flag to cifsFileInfo_put() to decide whether we should
  wait for running/pending oplock break handlers

* We keep an additionnal reference of the SMB FileInfo handle so that
  for the rest of the handler putting the handle won't close it.
  - The ref is bumped everytime we queue the handler via the
    cifs_queue_oplock_break() helper.
  - The ref is decremented at the end of the handler

This bug was triggered by xfstest 464.

Also important fix to address the various reports of
oops in smb2_push_mandatory_locks

Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
CC: Stable <stable@vger.kernel.org>

1 files changed, 25 insertions, 5 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 89006e044973..9c0ccc06d172 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -360,13 +360,31 @@ cifsFileInfo_get(struct cifsFileInfo *cifs_file)
 	return cifs_file;
 }
 
-/*
- * Release a reference on the file private data. This may involve closing
- * the filehandle out on the server. Must be called without holding
- * tcon->open_file_lock and cifs_file->file_info_lock.
+/**
+ * cifsFileInfo_put - release a reference of file priv data
+ *
+ * Always potentially wait for oplock handler. See _cifsFileInfo_put().
  */
 void cifsFileInfo_put(struct cifsFileInfo *cifs_file)
 {
+	_cifsFileInfo_put(cifs_file, true);
+}
+
+/**
+ * _cifsFileInfo_put - release a reference of file priv data
+ *
+ * This may involve closing the filehandle @cifs_file out on the
+ * server. Must be called without holding tcon->open_file_lock and
+ * cifs_file->file_info_lock.
+ *
+ * If @wait_for_oplock_handler is true and we are releasing the last
+ * reference, wait for any running oplock break handler of the file
+ * and cancel any pending one. If calling this function from the
+ * oplock break handler, you need to pass false.
+ *
+ */
+void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
+{
 	struct inode *inode = d_inode(cifs_file->dentry);
 	struct cifs_tcon *tcon = tlink_tcon(cifs_file->tlink);
 	struct TCP_Server_Info *server = tcon->ses->server;
@@ -414,7 +432,8 @@ void cifsFileInfo_put(struct cifsFileInfo *cifs_file)
 
 	spin_unlock(&tcon->open_file_lock);
 
-	oplock_break_cancelled = cancel_work_sync(&cifs_file->oplock_break);
+	oplock_break_cancelled = wait_oplock_handler ?
+		cancel_work_sync(&cifs_file->oplock_break) : false;
 
 	if (!tcon->need_reconnect && !cifs_file->invalidHandle) {
 		struct TCP_Server_Info *server = tcon->ses->server;
@@ -4603,6 +4622,7 @@ void cifs_oplock_break(struct work_struct *work)
 							     cinode);
 		cifs_dbg(FYI, "Oplock release rc = %d\n", rc);
 	}
+	_cifsFileInfo_put(cfile, false /* do not wait for ourself */);
 	cifs_done_oplock_break(cinode);
 }