ptrace: simplify ptrace_stop()->sigkill_pending() path

1. SIGKILL can't be blocked, remove this check from sigkill_pending().

2. When ptrace_stop() sees sigkill_pending() == T, it can just return.
   Kill "int killed" and simplify the code. This also is more correct,
   the tracer shouldn't see us in TASK_TRACED if we are not going to
   stop.

I strongly believe this code needs further changes.  We should do the "was
this task killed" check unconditionally, currently it depends on
arch_ptrace_stop_needed().  On the other hand, sigkill_pending() isn't
very clever.  If the task was killed tkill(SIGKILL), the signal can be
already dequeued if the caller is do_exit().

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 7 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index fdab7b363fa7..39c1706edf03 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1496,9 +1496,8 @@ static inline int may_ptrace_stop(void)
  */
 static int sigkill_pending(struct task_struct *tsk)
 {
-        return ((sigismember(&tsk->pending.signal, SIGKILL) ||
-                 sigismember(&tsk->signal->shared_pending.signal, SIGKILL)) &&
-                !unlikely(sigismember(&tsk->blocked, SIGKILL)));
+        return  sigismember(&tsk->pending.signal, SIGKILL) ||
+                sigismember(&tsk->signal->shared_pending.signal, SIGKILL);
 }
 
 /*
@@ -1514,8 +1513,6 @@ static int sigkill_pending(struct task_struct *tsk)
  */
 static void ptrace_stop(int exit_code, int clear_code, siginfo_t *info)
 {
-        int killed = 0;
-
         if (arch_ptrace_stop_needed(exit_code, info)) {
                 /*
                  * The arch code has something special to do before a
@@ -1531,7 +1528,8 @@ static void ptrace_stop(int exit_code, int clear_code, siginfo_t *info)
                 spin_unlock_irq(&current->sighand->siglock);
                 arch_ptrace_stop(exit_code, info);
                 spin_lock_irq(&current->sighand->siglock);
-                killed = sigkill_pending(current);
+                if (sigkill_pending(current))
+                        return;
         }
 
         /*
@@ -1548,7 +1546,7 @@ static void ptrace_stop(int exit_code, int clear_code, siginfo_t *info)
         __set_current_state(TASK_TRACED);
         spin_unlock_irq(&current->sighand->siglock);
         read_lock(&tasklist_lock);
-        if (!unlikely(killed) && may_ptrace_stop()) {
+        if (may_ptrace_stop()) {
                 do_notify_parent_cldstop(current, CLD_TRAPPED);
                 read_unlock(&tasklist_lock);
                 schedule();