2 files changed, 67 insertions, 1 deletions

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 515bff053de8..6ab80714a916 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -204,6 +204,41 @@ static inline void user_enable_block_step(struct task_struct *task)
 }
 #endif  /* arch_has_block_step */
 
+#ifndef arch_ptrace_stop_needed
+/**
+ * arch_ptrace_stop_needed - Decide whether arch_ptrace_stop() should be called
+ * @code:       current->exit_code value ptrace will stop with
+ * @info:       siginfo_t pointer (or %NULL) for signal ptrace will stop with
+ *
+ * This is called with the siglock held, to decide whether or not it's
+ * necessary to release the siglock and call arch_ptrace_stop() with the
+ * same @code and @info arguments.  It can be defined to a constant if
+ * arch_ptrace_stop() is never required, or always is.  On machines where
+ * this makes sense, it should be defined to a quick test to optimize out
+ * calling arch_ptrace_stop() when it would be superfluous.  For example,
+ * if the thread has not been back to user mode since the last stop, the
+ * thread state might indicate that nothing needs to be done.
+ */
+#define arch_ptrace_stop_needed(code, info)     (0)
+#endif
+
+#ifndef arch_ptrace_stop
+/**
+ * arch_ptrace_stop - Do machine-specific work before stopping for ptrace
+ * @code:       current->exit_code value ptrace will stop with
+ * @info:       siginfo_t pointer (or %NULL) for signal ptrace will stop with
+ *
+ * This is called with no locks held when arch_ptrace_stop_needed() has
+ * just returned nonzero.  It is allowed to block, e.g. for user memory
+ * access.  The arch can have machine-specific work to be done before
+ * ptrace stops.  On ia64, register backing store gets written back to user
+ * memory here.  Since this can be costly (requires dropping the siglock),
+ * we only do it when the arch requires it for this particular stop, as
+ * indicated by arch_ptrace_stop_needed().
+ */
+#define arch_ptrace_stop(code, info)            do { } while (0)
+#endif
+
 #endif
 
 #endif
diff --git a/kernel/signal.c b/kernel/signal.c
index e46971560fcb..5d30ff561847 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1578,6 +1578,17 @@ static inline int may_ptrace_stop(void)
 }
 
 /*
+ * Return nonzero if there is a SIGKILL that should be waking us up.
+ * Called with the siglock held.
+ */
+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)));
+}
+
+/*
  * This must be called with current->sighand->siglock held.
  *
  * This should be the path for all ptrace stops.
@@ -1590,6 +1601,26 @@ static inline int may_ptrace_stop(void)
  */
 static void ptrace_stop(int exit_code, int nostop_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
+                 * ptrace stop.  This is allowed to block, e.g. for faults
+                 * on user stack pages.  We can't keep the siglock while
+                 * calling arch_ptrace_stop, so we must release it now.
+                 * To preserve proper semantics, we must do this before
+                 * any signal bookkeeping like checking group_stop_count.
+                 * Meanwhile, a SIGKILL could come in before we retake the
+                 * siglock.  That must prevent us from sleeping in TASK_TRACED.
+                 * So after regaining the lock, we must check for SIGKILL.
+                 */
+                spin_unlock_irq(&current->sighand->siglock);
+                arch_ptrace_stop(exit_code, info);
+                spin_lock_irq(&current->sighand->siglock);
+                killed = sigkill_pending(current);
+        }
+
         /*
          * If there is a group stop in progress,
          * we must participate in the bookkeeping.
@@ -1605,7 +1636,7 @@ static void ptrace_stop(int exit_code, int nostop_code, siginfo_t *info)
         spin_unlock_irq(&current->sighand->siglock);
         try_to_freeze();
         read_lock(&tasklist_lock);
-        if (may_ptrace_stop()) {
+        if (!unlikely(killed) && may_ptrace_stop()) {
                 do_notify_parent_cldstop(current, CLD_TRAPPED);
                 read_unlock(&tasklist_lock);
                 schedule();