[PATCH v3] CIFS: keep FileInfo handle live during oplock break

[Aurelien Aptel <aaptel@suse.com>]

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.

Signed-off-by: Aurelien Aptel <aaptel@suse.com>
---
changes since v2:

* add _cifsFileInfo_put() and make cifsFileInfo_put() a wrapper of it

fs/cifs/cifsglob.h |  2 ++
 fs/cifs/file.c     | 30 +++++++++++++++++++++++++-----
 fs/cifs/misc.c     | 25 +++++++++++++++++++++++--
 fs/cifs/smb2misc.c |  6 +++---
 4 files changed, 53 insertions(+), 10 deletions(-)

diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 38feae812b47..ce0b1e8bc50c 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -1325,6 +1325,7 @@ cifsFileInfo_get_locked(struct cifsFileInfo *cifs_file)
 }
 
 struct cifsFileInfo *cifsFileInfo_get(struct cifsFileInfo *cifs_file);
+void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_hdlr);
 void cifsFileInfo_put(struct cifsFileInfo *cifs_file);
 
 #define CIFS_CACHE_READ_FLG	1
@@ -1847,6 +1848,7 @@ GLOBAL_EXTERN spinlock_t gidsidlock;
 #endif /* CONFIG_CIFS_ACL */
 
 void cifs_oplock_break(struct work_struct *work);
+void cifs_queue_oplock_break(struct cifsFileInfo *cfile);
 
 extern const struct slow_work_ops cifs_oplock_break_ops;
 extern struct workqueue_struct *cifsiod_wq;
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
@@ -360,12 +360,30 @@ 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);
@@ -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);
 }
 
diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
index bee203055b30..1e1626a2cfc3 100644
--- a/fs/cifs/misc.c
+++ b/fs/cifs/misc.c
@@ -501,8 +501,7 @@ 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);
@@ -607,6 +606,28 @@ 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);
diff --git a/fs/cifs/smb2misc.c b/fs/cifs/smb2misc.c
index 0e3570e40ff8..e311f58dc1c8 100644
--- a/fs/cifs/smb2misc.c
+++ b/fs/cifs/smb2misc.c
@@ -555,7 +555,7 @@ smb2_tcon_has_lease(struct cifs_tcon *tcon, struct smb2_lease_break *rsp,
 			clear_bit(CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2,
 				  &cinode->flags);
 
-		queue_work(cifsoplockd_wq, &cfile->oplock_break);
+		cifs_queue_oplock_break(cfile);
 		kfree(lw);
 		return true;
 	}
@@ -712,8 +712,8 @@ smb2_is_valid_oplock_break(char *buffer, struct TCP_Server_Info *server)
 					   CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2,
 					   &cinode->flags);
 				spin_unlock(&cfile->file_info_lock);
-				queue_work(cifsoplockd_wq,
-					   &cfile->oplock_break);
+
+				cifs_queue_oplock_break(cfile);
 
 				spin_unlock(&tcon->open_file_lock);
 				spin_unlock(&cifs_tcp_ses_lock);
-- 
2.16.4