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SubjectRe: PPP is not SMP safe in 2.2.X (fix)

I use PPP on an SMP box to get an xDSL link up. So PPP uses
a pty instead of a serial port to write data to. A userland
daemon -- pptp -- reads the pty, does some hdlc-to-gre conversion,
and send the result to the xDSL modem directly.

Everything goes fine on uni-processor. On SMP, pptp often gets
confused when dealing with outgoing packets coming from masqueraded hosts
(the SMP box acts as a firewall in my configuration).

The data that pptp reads from the pty have bad FCS, and the xDSL link
promptly crashes. I assume that this problem comes from a race condition
in the ppp code or the masquerading code (but both ipchains et netfilter
trigger the bug).

Paul Mackerras's and Oleg's patches didn't solve the problem : I
also tried to extend the fix in ldisc calling from serial.c to
pty.c without more success.

Suggestions to fix this behaviour are welcome :-)


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