cifs: prevent cifsd from exiting prematurely

When cifs_demultiplex_thread exits, it does a number of cleanup tasks
including freeing the TCP_Server_Info struct. Much of the existing code
in cifs assumes that when there is a cisfSesInfo struct, that it holds a
reference to a valid TCP_Server_Info struct.

We can never allow cifsd to exit when a cifsSesInfo struct is still
holding a reference to the server. The server pointers will then point
to freed memory.

This patch eliminates a couple of questionable conditions where it does
this.  The idea here is to make an -EINTR return from kernel_recvmsg
behave the same way as -ERESTARTSYS or -EAGAIN. If the task was
signalled from cifs_put_tcp_session, then tcpStatus will be CifsExiting,
and the kernel_recvmsg call will return quickly.

There's also another condition where this can occur too -- if the
tcpStatus is still in CifsNew, then it will also exit if the server
closes the socket prematurely.  I think we'll probably also need to fix
that situation, but that requires a bit more consideration.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 0ea52e9..5f68b96 100644 (file)
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -400,7 +400,9 @@ incomplete_rcv:
                        cFYI(1, "call to reconnect done");
                        csocket = server->ssocket;
                        continue;
-               } else if ((length == -ERESTARTSYS) || (length == -EAGAIN)) {
+               } else if (length == -ERESTARTSYS ||
+                          length == -EAGAIN ||
+                          length == -EINTR) {
                        msleep(1); /* minimum sleep to prevent looping
                                allowing socket to clear and app threads to set
                                tcpStatus CifsNeedReconnect if server hung */
@@ -422,10 +424,6 @@ incomplete_rcv:
                                   and so simply return error to mount */
                                break;
                        }
-                       if (!try_to_freeze() && (length == -EINTR)) {
-                               cFYI(1, "cifsd thread killed");
-                               break;
-                       }
                        cFYI(1, "Reconnect after unexpected peek error %d",
                                length);
                        cifs_reconnect(server);
@@ -522,8 +520,7 @@ incomplete_rcv:
                     total_read += length) {
                        length = kernel_recvmsg(csocket, &smb_msg, &iov, 1,
                                                pdu_length - total_read, 0);
-                       if ((server->tcpStatus == CifsExiting) ||
-                           (length == -EINTR)) {
+                       if (server->tcpStatus == CifsExiting) {
                                /* then will exit */
                                reconnect = 2;
                                break;
@@ -534,8 +531,9 @@ incomplete_rcv:
                                /* Now we will reread sock */
                                reconnect = 1;
                                break;
-                       } else if ((length == -ERESTARTSYS) ||
-                                  (length == -EAGAIN)) {
+                       } else if (length == -ERESTARTSYS ||
+                                  length == -EAGAIN ||
+                                  length == -EINTR) {
                                msleep(1); /* minimum sleep to prevent looping,
                                              allowing socket to clear and app
                                              threads to set tcpStatus