[PATCH] threading fix, tid-2.5.47-A3

This introduces the sys_set_thread_address() syscall.  It sets the tid
address (which gets cleared at VM release time) and returns the PID so
that the newly initialized 'initial thread' does not have to do an
additional sys_gettid() call.

It is used to bootstrap a thread group where the original thread user
hasn't had a tid address assigned to it by any parent.

arch/i386/kernel/entry.S

@@ -767,6 +767,7 @@ ENTRY(sys_call_table)
 	.long sys_epoll_ctl	/* 255 */
 	.long sys_epoll_wait
  	.long sys_remap_file_pages
+ 	.long sys_set_tid_address
 
 
 	.rept NR_syscalls-(.-sys_call_table)/4

kernel/fork.c

@@ -679,6 +679,13 @@ static inline void copy_flags(unsigned long clone_flags, struct task_struct *p)
 	p->flags = new_flags;
 }
 
+asmlinkage int sys_set_tid_address(int *user_tid)
+{
+	current->user_tid = user_tid;
+
+	return current->pid;
+}
+
 /*
  * This creates a new process as a copy of the old one,
  * but does not actually start it yet.