RE: [PATCH 5.2 02/45] smb3: fix unmount hang in open_shroot

[Pavel Shilovskiy]

Hi Greg,

Are you going to apply this patch to the 5.3.y stable kernel? The patch is applicable there too.

Best regards,
Pavel Shilovsky

-----Original Message-----
From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> 
Sent: Sunday, September 29, 2019 6:56 AM
To: linux-kernel@xxxxxxxxxxxxxxx
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>; stable@xxxxxxxxxxxxxxx; kbuild test robot <lkp@xxxxxxxxx>; Dan Carpenter <dan.carpenter@xxxxxxxxxx>; Pavel Shilovskiy <pshilov@xxxxxxxxxxxxx>; Steven French <Steven.French@xxxxxxxxxxxxx>; Aurelien Aptel <aaptel@xxxxxxxx>; Sasha Levin <sashal@xxxxxxxxxx>
Subject: [PATCH 5.2 02/45] smb3: fix unmount hang in open_shroot

From: Steve French <stfrench@xxxxxxxxxxxxx>

[ Upstream commit 96d9f7ed00b86104bf03adeffc8980897e9694ab ]

An earlier patch "CIFS: fix deadlock in cached root handling"
did not completely address the deadlock in open_shroot. This patch addresses the deadlock.

In testing the recent patch:
  smb3: improve handling of share deleted (and share recreated) we were able to reproduce the open_shroot deadlock to one of the target servers in unmount in a delete share scenario.

Fixes: 7e5a70ad88b1e ("CIFS: fix deadlock in cached root handling")

This is version 2 of this patch. An earlier version of this patch "smb3: fix unmount hang in open_shroot" had a problem found by Dan.

Reported-by: kbuild test robot <lkp@xxxxxxxxx>
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

Suggested-by: Pavel Shilovsky <pshilov@xxxxxxxxxxxxx>
Reviewed-by: Pavel Shilovsky <pshilov@xxxxxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
CC: Aurelien Aptel <aaptel@xxxxxxxx>
CC: Stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/cifs/smb2ops.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c index 42de31d206169..8ae8ef526b4a5 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -656,6 +656,15 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
 		return 0;
 	}
 
+	/*
+	 * We do not hold the lock for the open because in case
+	 * SMB2_open needs to reconnect, it will end up calling
+	 * cifs_mark_open_files_invalid() which takes the lock again
+	 * thus causing a deadlock
+	 */
+
+	mutex_unlock(&tcon->crfid.fid_mutex);
+
 	if (smb3_encryption_required(tcon))
 		flags |= CIFS_TRANSFORM_REQ;
 
@@ -677,7 +686,7 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
 
 	rc = SMB2_open_init(tcon, &rqst[0], &oplock, &oparms, &utf16_path);
 	if (rc)
-		goto oshr_exit;
+		goto oshr_free;
 	smb2_set_next_command(tcon, &rqst[0]);
 
 	memset(&qi_iov, 0, sizeof(qi_iov));
@@ -690,18 +699,10 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
 				  sizeof(struct smb2_file_all_info) +
 				  PATH_MAX * 2, 0, NULL);
 	if (rc)
-		goto oshr_exit;
+		goto oshr_free;
 
 	smb2_set_related(&rqst[1]);
 
-	/*
-	 * We do not hold the lock for the open because in case
-	 * SMB2_open needs to reconnect, it will end up calling
-	 * cifs_mark_open_files_invalid() which takes the lock again
-	 * thus causing a deadlock
-	 */
-
-	mutex_unlock(&tcon->crfid.fid_mutex);
 	rc = compound_send_recv(xid, ses, flags, 2, rqst,
 				resp_buftype, rsp_iov);
 	mutex_lock(&tcon->crfid.fid_mutex);
--
2.20.1