[PATCH] threading enhancements, tid-2.5.48-C0

Support more flexible child pid set/clear operations for NPTL.

there's one more improvement in the interface: set the parent-TID prior
doing the copy_mm() - this helps cfork() to pass the TID to the child as
well.

2 files changed, 24 insertions, 22 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index f89734b831ac..27cf572cedf8 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -408,16 +408,16 @@ void mm_release(void)
 		tsk->vfork_done = NULL;
 		complete(vfork_done);
 	}
-	if (tsk->user_tid) {
-		int * user_tid = tsk->user_tid;
-		tsk->user_tid = NULL;
+	if (tsk->clear_child_tid) {
+		int * tidptr = tsk->clear_child_tid;
+		tsk->clear_child_tid = NULL;
 
 		/*
 		 * We dont check the error code - if userspace has
 		 * not set up a proper pointer then tough luck.
 		 */
-		put_user(0, user_tid);
-		sys_futex((unsigned long)user_tid, FUTEX_WAKE, 1, NULL);
+		put_user(0, tidptr);
+		sys_futex((unsigned long)tidptr, FUTEX_WAKE, 1, NULL);
 	}
 }
 
@@ -680,9 +680,9 @@ 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)
+asmlinkage int sys_set_tid_address(int *tidptr)
 {
-	current->user_tid = user_tid;
+	current->clear_child_tid = tidptr;
 
 	return current->pid;
 }
@@ -699,7 +699,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 			    unsigned long stack_start,
 			    struct pt_regs *regs,
 			    unsigned long stack_size,
-			    int *user_tid)
+			    int *parent_tidptr,
+			    int *child_tidptr)
 {
 	int retval;
 	struct task_struct *p = NULL;
@@ -766,6 +767,11 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 		if (p->pid == -1)
 			goto bad_fork_cleanup;
 	}
+	retval = -EFAULT;
+	if (clone_flags & CLONE_PARENT_SETTID)
+		if (put_user(p->pid, parent_tidptr))
+			goto bad_fork_cleanup;
+
 	p->proc_dentry = NULL;
 
 	INIT_LIST_HEAD(&p->run_list);
@@ -823,19 +829,14 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	retval = copy_thread(0, clone_flags, stack_start, stack_size, p, regs);
 	if (retval)
 		goto bad_fork_cleanup_namespace;
-	/*
-	 * Notify the child of the TID?
-	 */
-	retval = -EFAULT;
-	if (clone_flags & CLONE_SETTID)
-		if (put_user(p->pid, user_tid))
-			goto bad_fork_cleanup_namespace;
 
+	if (clone_flags & CLONE_CHILD_SETTID)
+		p->set_child_tid = child_tidptr;
 	/*
-	 * Does the userspace VM want the TID cleared on mm_release()?
+	 * Clear TID on mm_release()?
 	 */
-	if (clone_flags & CLONE_CLEARTID)
-		p->user_tid = user_tid;
+	if (clone_flags & CLONE_CHILD_CLEARTID)
+		p->clear_child_tid = child_tidptr;
 
 	/*
 	 * Syscall tracing should be turned off in the child regardless
@@ -1004,7 +1005,8 @@ struct task_struct *do_fork(unsigned long clone_flags,
 			    unsigned long stack_start,
 			    struct pt_regs *regs,
 			    unsigned long stack_size,
-			    int *user_tid)
+			    int *parent_tidptr,
+			    int *child_tidptr)
 {
 	struct task_struct *p;
 	int trace = 0;
@@ -1015,7 +1017,7 @@ struct task_struct *do_fork(unsigned long clone_flags,
 			clone_flags |= CLONE_PTRACE;
 	}
 
-	p = copy_process(clone_flags, stack_start, regs, stack_size, user_tid);
+	p = copy_process(clone_flags, stack_start, regs, stack_size, parent_tidptr, child_tidptr);
 	if (!IS_ERR(p)) {
 		struct completion vfork;
 
diff --git a/kernel/sched.c b/kernel/sched.c
index 6d0ac320bcbc..b446ce8eecc1 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -503,12 +503,12 @@ void sched_exit(task_t * p)
  * schedule_tail - first thing a freshly forked thread must call.
  * @prev: the thread we just switched away from.
  */
-#if CONFIG_SMP || CONFIG_PREEMPT
 asmlinkage void schedule_tail(task_t *prev)
 {
 	finish_arch_switch(this_rq(), prev);
+	if (current->set_child_tid)
+		put_user(current->pid, current->set_child_tid);
 }
-#endif
 
 /*
  * context_switch - switch to the new MM and the new