[PATCH 16/31] reintroduce tracehook_finish_jctl() as utrace_end_stop()

[Oleg Nesterov]

utrace_finish_stop() is needed to avoid the races with SIGKILL which
wakes up UTRACED task, and thus it should be called every time after
the STOPPED/TRACED/UTRACED returns from schedule(), remember that
TASK_UTRACED can be added while the task is STOPPED/UTRACED.

- change do_signal_state() to call this helper right after schedule(),
  otherwise this logic is broken by the upstream changes

- now that utrace doesn't control TASK_TRACED bit, ptrace_stop() must
  call this helper too.

Signed-off-by: Oleg Nesterov <oleg at redhat.com>
---
 include/linux/utrace.h |   11 +++++++++++
 kernel/signal.c        |    5 +++++
 kernel/utrace.c        |    2 +-
 3 files changed, 17 insertions(+), 1 deletions(-)

diff --git a/include/linux/utrace.h b/include/linux/utrace.h
index cf13839..0279c74 100644
--- a/include/linux/utrace.h
+++ b/include/linux/utrace.h
@@ -719,4 +719,15 @@ static inline void utrace_exit_notify(struct task_struct *task,
 		utrace_report_death(task, group_dead, signal);
 }
 
+/**
+ * utrace_end_stop - report about return from STOPPED/TRACED
+ *
+ * This is called by do_signal_stop() and ptrace_stop after wakeup.
+ */
+static inline void utrace_end_stop(void)
+{
+	if (task_utrace_flags(current))
+		utrace_finish_stop();
+}
+
 #endif	/* linux/utrace.h */
diff --git a/kernel/signal.c b/kernel/signal.c
index 0dc6abb..a625309 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1895,6 +1895,8 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
 		read_unlock(&tasklist_lock);
 	}
 
+	utrace_end_stop();
+
 	/*
 	 * While in TASK_TRACED, we were considered "frozen enough".
 	 * Now that we woke up, it's crucial if we're supposed to be
@@ -2059,6 +2061,9 @@ static bool do_signal_stop(int signr)
 
 		/* Now we don't run again until woken by SIGCONT or SIGKILL */
 		schedule();
+
+		utrace_end_stop();
+
 		return true;
 	} else {
 		/*
diff --git a/kernel/utrace.c b/kernel/utrace.c
index 2097103..d41b982 100644
--- a/kernel/utrace.c
+++ b/kernel/utrace.c
@@ -741,7 +741,7 @@ static bool utrace_reset(struct task_struct *task, struct utrace *utrace)
 void utrace_finish_stop(void)
 {
 	/*
-	 * If we were task_is_traced() and then SIGKILL'ed, make
+	 * If we were task_is_utraced() and then SIGKILL'ed, make
 	 * sure we do nothing until the tracer drops utrace->lock.
 	 */
 	if (unlikely(__fatal_signal_pending(current))) {
-- 
1.5.5.1