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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>
This commit is contained in:
Jeff Layton 2010-09-03 12:00:49 -04:00 committed by Steve French
parent 4266d9118f
commit 522bbe65a2
1 changed files with 7 additions and 9 deletions
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16
fs/cifs/connect.c
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@ -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