[PATCH] smb3: fix unmount hang in open_shroot

[Steve French <smfrench@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 1915 bytes --]

smb3: fix unmount hang in open_shroot

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")

Suggested-by: Pavel Shilovsky <pshilov@microsoft.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
CC: Aurelien Aptel <aaptel@suse.com>
CC: Stable <stable@vger.kernel.org>
---
 fs/cifs/smb2ops.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index 3672ce0bfbaf..150327ebb2b4 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -658,6 +658,15 @@ 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;

@@ -696,14 +705,6 @@ int open_shroot(unsigned int xid, struct
cifs_tcon *tcon, struct cifs_fid *pfid)

  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);

--
Thanks,

Steve

[-- Attachment #2: 0001-smb3-fix-unmount-hang-in-open_shroot.patch --]
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From 1f16bb0483a133882dc2f405dfcc26daa30b9117 Mon Sep 17 00:00:00 2001
From: Steve French <stfrench@microsoft.com>
Date: Thu, 12 Sep 2019 17:52:54 -0500
Subject: [PATCH] smb3: fix unmount hang in open_shroot

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")

Suggested-by: Pavel Shilovsky <pshilov@microsoft.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
CC: Aurelien Aptel <aaptel@suse.com>
CC: Stable <stable@vger.kernel.org>
---
 fs/cifs/smb2ops.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index 3672ce0bfbaf..150327ebb2b4 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -658,6 +658,15 @@ 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;
 
@@ -696,14 +705,6 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
 
 	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