kill PT_ATTACHED

Since the patch

	"Fix ptrace_attach()/ptrace_traceme()/de_thread() race"
	commit f5b40e363a

we set PT_ATTACHED and change child->parent "atomically" wrt task_list lock.

This means we can remove the checks like "PT_ATTACHED && ->parent != ptracer"
which were needed to catch the "ptrace attach is in progress" case.  We can
also remove the flag itself since nobody else uses it.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/ptrace.h

@@ -67,7 +67,6 @@
 #define PT_TRACE_EXEC	0x00000080
 #define PT_TRACE_VFORK_DONE	0x00000100
 #define PT_TRACE_EXIT	0x00000200
-#define PT_ATTACHED	0x00000400	/* parent != real_parent */
 
 #define PT_TRACE_MASK	0x000003f4
 

kernel/exit.c

@@ -1514,18 +1514,7 @@ static int wait_task_continued(struct task_struct *p, int noreap,
 
 static inline int my_ptrace_child(struct task_struct *p)
 {
-	if (!(p->ptrace & PT_PTRACED))
-		return 0;
-	if (!(p->ptrace & PT_ATTACHED))
-		return 1;
-	/*
-	 * This child was PTRACE_ATTACH'd.  We should be seeing it only if
-	 * we are the attacher.  If we are the real parent, this is a race
-	 * inside ptrace_attach.  It is waiting for the tasklist_lock,
-	 * which we have to switch the parent links, but has already set
-	 * the flags in p->ptrace.
-	 */
-	return (p->parent != p->real_parent);
+	return p->ptrace & PT_PTRACED;
 }
 
 static long do_wait(pid_t pid, int options, struct siginfo __user *infop,

kernel/ptrace.c

@@ -100,8 +100,7 @@ int ptrace_check_attach(struct task_struct *child, int kill)
 	 */
 	read_lock(&tasklist_lock);
 	if ((child->ptrace & PT_PTRACED) && child->parent == current &&
-	    (!(child->ptrace & PT_ATTACHED) || child->real_parent != current)
-	    && child->signal != NULL) {
+	     child->signal != NULL) {
 		ret = 0;
 		spin_lock_irq(&child->sighand->siglock);
 		if (task_is_stopped(child))
@@ -200,8 +199,7 @@ repeat:
 		goto bad;
 
 	/* Go */
-	task->ptrace |= PT_PTRACED | ((task->real_parent != current)
-				      ? PT_ATTACHED : 0);
+	task->ptrace |= PT_PTRACED;
 	if (capable(CAP_SYS_PTRACE))
 		task->ptrace |= PT_PTRACE_CAP;
 

kernel/signal.c

@@ -1556,11 +1556,6 @@ static inline int may_ptrace_stop(void)
 {
 	if (!likely(current->ptrace & PT_PTRACED))
 		return 0;
-
-	if (unlikely(current->parent == current->real_parent &&
-		    (current->ptrace & PT_ATTACHED)))
-		return 0;
-
 	/*
 	 * Are we in the middle of do_coredump?
 	 * If so and our tracer is also part of the coredump stopping