MIPS: Don't stomp on caller's ->regs[2] in copy_thread()

We never needed that (->regs[2] is overwritten on return from syscall paths
with return value of syscall, so storing it there early made no sense) and
with new restart logics since d27240b it
has become really bad - we lose the original syscall number before the
place where we decide that we might need a syscall restart.

Note that for child we do need the assignment to regs[2] - it won't go
through the normal return from syscall path.

[Ralf: Issue found and reported by Lluís; initial investigations by me;
bug finally found and patch by Al; testing by me and Lluís.]

Signed-off-by: Al Viro <[email protected]>
Tested-by: Lluís Batlle i Rossell <[email protected]>
Signed-off-by: Ralf Baechle <[email protected]>

arch/mips/kernel/process.c

@@ -142,7 +142,6 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
 	childregs->regs[7] = 0;	/* Clear error flag */
 
 	childregs->regs[2] = 0;	/* Child gets zero as return value */
-	regs->regs[2] = p->pid;
 
 	if (childregs->cp0_status & ST0_CU0) {
 		childregs->regs[28] = (unsigned long) ti;