kill PT_ATTACHED

Since the patch

	"Fix ptrace_attach()/ptrace_traceme()/de_thread() race"
	commit f5b40e363ad6041a96e3da32281d8faa191597b9

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>

4 files changed, 3 insertions, 22 deletions

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 6ab80714a916..ebe0c17039cf 100644
--- a/include/linux/ptrace.h
+++ b/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
 
diff --git a/kernel/exit.c b/kernel/exit.c
index eb9934a82fc1..1f2c15297f2d 100644
--- a/kernel/exit.c
+++ b/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,
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 628b03ab88a5..2dc00298e678 100644
--- a/kernel/ptrace.c
+++ b/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;
 
diff --git a/kernel/signal.c b/kernel/signal.c
index 5d30ff561847..6d6d1ab39e7e 100644
--- a/kernel/signal.c
+++ b/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