CIFS: keep FileInfo handle live during oplock break

commit b98749cac4a695f084a5ff076f4510b23e353ecd upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 23 insertions, 2 deletions

diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
index 6926685e513c..facc94e159a1 100644
--- a/fs/cifs/misc.c
+++ b/fs/cifs/misc.c
@@ -490,8 +490,7 @@ is_valid_oplock_break(char *buffer, struct TCP_Server_Info *srv)
 					   CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2,
 					   &pCifsInode->flags);
 
-				queue_work(cifsoplockd_wq,
-					   &netfile->oplock_break);
+				cifs_queue_oplock_break(netfile);
 				netfile->oplock_break_cancelled = false;
 
 				spin_unlock(&tcon->open_file_lock);
@@ -588,6 +587,28 @@ void cifs_put_writer(struct cifsInodeInfo *cinode)
 	spin_unlock(&cinode->writers_lock);
 }
 
+/**
+ * cifs_queue_oplock_break - queue the oplock break handler for cfile
+ *
+ * This function is called from the demultiplex thread when it
+ * receives an oplock break for @cfile.
+ *
+ * Assumes the tcon->open_file_lock is held.
+ * Assumes cfile->file_info_lock is NOT held.
+ */
+void cifs_queue_oplock_break(struct cifsFileInfo *cfile)
+{
+	/*
+	 * Bump the handle refcount now while we hold the
+	 * open_file_lock to enforce the validity of it for the oplock
+	 * break handler. The matching put is done at the end of the
+	 * handler.
+	 */
+	cifsFileInfo_get(cfile);
+
+	queue_work(cifsoplockd_wq, &cfile->oplock_break);
+}
+
 void cifs_done_oplock_break(struct cifsInodeInfo *cinode)
 {
 	clear_bit(CIFS_INODE_PENDING_OPLOCK_BREAK, &cinode->flags);