[PATCH v3 4/6] ptrace: Track __TASK_TRACED state in p->ptrace

[Peter Zijlstra <peterz@infradead.org>]

Just like we can recover __TASK_STOPPED from p->jobctl, add some bits
to p->ptrace such that we can recover __TASK_TRACED.

All these t->ptrace modifications are done under sighand lock.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 include/linux/ptrace.h       |    4 ++++
 include/linux/sched/signal.h |    6 ++----
 kernel/ptrace.c              |   27 ++++++++++++++++++---------
 kernel/signal.c              |    1 +
 4 files changed, 25 insertions(+), 13 deletions(-)

--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -45,6 +45,10 @@ extern int ptrace_access_vm(struct task_
 #define PT_TRACE_SECCOMP	PT_EVENT_FLAG(PTRACE_EVENT_SECCOMP)	        // 0x00000400
 
 #define PT_SEIZED		0x00010000 /* SEIZE used, enable new behavior */// 0x00010000
+#define PT_STOPPED		0x00020000					// 0x00020000
+#define PT_STOPPED_FATAL	0x00040000					// 0x00040000
+
+#define PT_STOPPED_MASK		(PT_STOPPED|PT_STOPPED_FATAL)
 
 #define PT_EXITKILL		(PTRACE_O_EXITKILL << PT_OPT_FLAG_SHIFT)	// 0x00800000
 #define PT_SUSPEND_SECCOMP	(PTRACE_O_SUSPEND_SECCOMP << PT_OPT_FLAG_SHIFT) // 0x01000000
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -418,10 +418,8 @@ static inline void signal_wake_up(struct
 {
 	signal_wake_up_state(t, resume ? TASK_WAKEKILL : 0);
 }
-static inline void ptrace_signal_wake_up(struct task_struct *t, bool resume)
-{
-	signal_wake_up_state(t, resume ? __TASK_TRACED : 0);
-}
+
+extern void ptrace_signal_wake_up(struct task_struct *t, bool resume);
 
 void task_join_group_stop(struct task_struct *task);
 
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -64,6 +64,14 @@ int ptrace_access_vm(struct task_struct
 	return ret;
 }
 
+void ptrace_signal_wake_up(struct task_struct *t, bool resume)
+{
+	lockdep_assert_task_sighand_held(t);
+
+	if (resume)
+		t->ptrace &= ~PT_STOPPED_MASK;
+	signal_wake_up_state(t, resume ? __TASK_TRACED : 0);
+}
 
 void __ptrace_link(struct task_struct *child, struct task_struct *new_parent,
 		   const struct cred *ptracer_cred)
@@ -197,6 +205,8 @@ static bool ptrace_freeze_traced(struct
 	spin_lock_irq(&task->sighand->siglock);
 	if (task_is_traced(task) && !looks_like_a_spurious_pid(task) &&
 	    !__fatal_signal_pending(task)) {
+		task->ptrace &= ~PT_STOPPED_MASK;
+		task->ptrace |= PT_STOPPED;
 		WRITE_ONCE(task->__state, __TASK_TRACED);
 		ret = true;
 	}
@@ -218,10 +228,13 @@ static void ptrace_unfreeze_traced(struc
 	 */
 	spin_lock_irq(&task->sighand->siglock);
 	if (READ_ONCE(task->__state) == __TASK_TRACED) {
-		if (__fatal_signal_pending(task))
+		if (__fatal_signal_pending(task)) {
+			task->ptrace &= ~PT_STOPPED_MASK;
 			wake_up_state(task, __TASK_TRACED);
-		else
+		} else {
+			task->ptrace |= PT_STOPPED_MASK;
 			WRITE_ONCE(task->__state, TASK_TRACED);
+		}
 	}
 	spin_unlock_irq(&task->sighand->siglock);
 }
@@ -835,8 +848,6 @@ static long ptrace_get_rseq_configuratio
 static int ptrace_resume(struct task_struct *child, long request,
 			 unsigned long data)
 {
-	bool need_siglock;
-
 	if (!valid_signal(data))
 		return -EIO;
 
@@ -877,13 +888,11 @@ static int ptrace_resume(struct task_str
 	 * status and clears the code too; this can't race with the tracee, it
 	 * takes siglock after resume.
 	 */
-	need_siglock = data && !thread_group_empty(current);
-	if (need_siglock)
-		spin_lock_irq(&child->sighand->siglock);
+	spin_lock_irq(&child->sighand->siglock);
 	child->exit_code = data;
+	child->ptrace &= ~PT_STOPPED_MASK;
 	wake_up_state(child, __TASK_TRACED);
-	if (need_siglock)
-		spin_unlock_irq(&child->sighand->siglock);
+	spin_unlock_irq(&child->sighand->siglock);
 
 	return 0;
 }
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2228,6 +2228,7 @@ static void ptrace_stop(int exit_code, i
 			return;
 	}
 
+	current->ptrace |= PT_STOPPED_MASK;
 	set_special_state(TASK_TRACED);
 
 	/*