[linux-cifs-client] re: SYN_RECV flood

[Steve French]

> I'm using the cifs module 1.17c on kernel 2.4.21 in Red Hat Enterprise
> 3. Occasionally when a user mounts their home directory and begins
> running code that's somewhat network-intensive, the cifs module will
> start flooding the server (Samba 3.0.5) with SYN_RECV packets. It
> doesn't stop if I manually kill the process, but does stop immediately
> if I unmount the share. After I unmount the share and the user remounts
> it, everything works perfectly again for a random amount of time until
> it happens again. 
> 

This looks like it is caused by cifsd repeatedly reconnecting while
SIGKILL is pending.   When the cifsd (smb demultiplex thread) receives a
kill signal which it can in one rare unmount case and in a case when the
user misspells the user name on mount, when there is already a mount
with a different userid on that client - the cifsd thread starts
gettting EINTR back and thus looping in reconnect code.  I have just
fixed that in the bk://cifs.bkbits.net/linux-2.5cifs tree and will
create a 2.4 version with this in the next few days.

This is very likely the issue that you are running into.