2007-11-21 16:00:43

by Oleg Nesterov

Subject: [PATCH -mm 1/3] 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 <[email protected]>

--- PT/include/linux/ptrace.h~1_PT_ATTACHED 2007-11-21 16:41:25.000000000 +0300
+++ PT/include/linux/ptrace.h 2007-11-21 16:50:39.000000000 +0300
@@ -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

--- PT/kernel/ptrace.c~1_PT_ATTACHED 2007-11-21 16:41:25.000000000 +0300
+++ PT/kernel/ptrace.c 2007-11-21 16:53:39.000000000 +0300
@@ -100,8 +100,7 @@ int ptrace_check_attach(struct task_stru
*/
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 (is_task_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;

--- PT/kernel/signal.c~1_PT_ATTACHED 2007-11-21 16:41:25.000000000 +0300
+++ PT/kernel/signal.c 2007-11-21 16:50:39.000000000 +0300
@@ -1577,11 +1577,6 @@ 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
--- PT/kernel/exit.c~1_PT_ATTACHED 2007-11-21 16:41:25.000000000 +0300
+++ PT/kernel/exit.c 2007-11-21 16:50:39.000000000 +0300
@@ -1511,18 +1511,7 @@ static int wait_task_continued(struct ta

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,

2007-12-11 01:18:48

by Roland McGrath

Subject: Re: [PATCH -mm 1/3] kill PT_ATTACHED

Starting to catch up on some old patch review today. This one has my ACK.


Thanks,
Roland