linux-kernel - [PATCH 5.1 014/121] cifs: fix GlobalMid_Lock bug in cifs

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Date:   Mon, 24 Jun 2019 17:55:46 +0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ronnie Sahlberg <lsahlber@...hat.com>,
        Pavel Shilovsky <pshilov@...rosoft.com>,
        Steve French <stfrench@...rosoft.com>
Subject: [PATCH 5.1 014/121] cifs: fix GlobalMid_Lock bug in cifs_reconnect

From: Ronnie Sahlberg <lsahlber@...hat.com>

commit 61cabc7b0a5cf0d3c532cfa96594c801743fe7f6 upstream.

We can not hold the GlobalMid_Lock spinlock during the
dfs processing in cifs_reconnect since it invokes things that may sleep
and thus trigger :

BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:23

Thus we need to drop the spinlock during this code block.

RHBZ: 1716743

Cc: stable@...r.kernel.org
Signed-off-by: Ronnie Sahlberg <lsahlber@...hat.com>
Acked-by: Pavel Shilovsky <pshilov@...rosoft.com>
Signed-off-by: Steve French <stfrench@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/cifs/connect.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -478,6 +478,7 @@ cifs_reconnect(struct TCP_Server_Info *s
 	spin_lock(&GlobalMid_Lock);
 	server->nr_targets = 1;
 #ifdef CONFIG_CIFS_DFS_UPCALL
+	spin_unlock(&GlobalMid_Lock);
 	cifs_sb = find_super_by_tcp(server);
 	if (IS_ERR(cifs_sb)) {
 		rc = PTR_ERR(cifs_sb);
@@ -495,6 +496,7 @@ cifs_reconnect(struct TCP_Server_Info *s
 	}
 	cifs_dbg(FYI, "%s: will retry %d target(s)\n", __func__,
 		 server->nr_targets);
+	spin_lock(&GlobalMid_Lock);
 #endif
 	if (server->tcpStatus == CifsExiting) {
 		/* the demux thread will exit normally