ptrace: relocate set_current_state(TASK_TRACED) in ptrace_stop()

In ptrace_stop(), after arch hook is done, the task state and jobctl
bits are updated while holding siglock.  The ordering requirement
there is that TASK_TRACED is set before JOBCTL_TRAPPING is cleared to
prevent ptracer waiting on TRAPPING doesn't end up waking up TRACED is
actually set and sees TASK_RUNNING in wait(2).

Move set_current_state(TASK_TRACED) to the top of the block and
reorganize comments.  This makes the ordering more obvious
(TASK_TRACED before other updates) and helps future updates to group
stop participation.

This patch doesn't cause any functional change.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>

1 files changed, 13 insertions, 15 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index ab6851c06461..62a6c3bb9f0d 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1733,6 +1733,18 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
         }
 
         /*
+         * We're committing to trapping.  TRACED should be visible before
+         * TRAPPING is cleared; otherwise, the tracer might fail do_wait().
+         * Also, transition to TRACED and updates to ->jobctl should be
+         * atomic with respect to siglock and should be done after the arch
+         * hook as siglock is released and regrabbed across it.
+         */
+        set_current_state(TASK_TRACED);
+
+        current->last_siginfo = info;
+        current->exit_code = exit_code;
+
+        /*
          * If @why is CLD_STOPPED, we're trapping to participate in a group
          * stop.  Do the bookkeeping.  Note that if SIGCONT was delievered
          * while siglock was released for the arch hook, PENDING could be
@@ -1742,21 +1754,7 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
         if (why == CLD_STOPPED && (current->jobctl & JOBCTL_STOP_PENDING))
                 gstop_done = task_participate_group_stop(current);
 
-        current->last_siginfo = info;
-        current->exit_code = exit_code;
-
-        /*
-         * TRACED should be visible before TRAPPING is cleared; otherwise,
-         * the tracer might fail do_wait().
-         */
-        set_current_state(TASK_TRACED);
-
-        /*
-         * We're committing to trapping.  Clearing JOBCTL_TRAPPING and
-         * transition to TASK_TRACED should be atomic with respect to
-         * siglock.  This should be done after the arch hook as siglock is
-         * released and regrabbed across it.
-         */
+        /* entering a trap, clear TRAPPING */
         task_clear_jobctl_trapping(current);
 
         spin_unlock_irq(&current->sighand->siglock);