tracehook: release_task

This moves the ptrace-related logic from release_task into tracehook.h and
ptrace.h inlines.  It provides clean hooks both before and after locking
tasklist_lock, for future tracing logic to do more cleanup without the
lock.

This also changes release_task() itself in the rare "zap_leader" case to
set the leader to EXIT_DEAD before iterating.  This maintains the
invariant that release_task() only ever handles a task in EXIT_DEAD.  This
is a common-sense invariant that is already always true except in this one
arcane case of zombie leader whose parent ignores SIGCHLD.

This change is harmless and only costs one store in this one rare case.
It keeps the expected state more consisently sane, which is nicer when
debugging weirdness in release_task().  It also lets some future code in
the tracehook entry points rely on this invariant for bookkeeping.

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

1 files changed, 13 insertions, 0 deletions

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index dae6d85520fb..ed69c03692d9 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -176,6 +176,19 @@ static inline void ptrace_init_task(struct task_struct *child, bool ptrace)
         }
 }
 
+/**
+ * ptrace_release_task - final ptrace-related cleanup of a zombie being reaped
+ * @task:       task in %EXIT_DEAD state
+ *
+ * Called with write_lock(&tasklist_lock) held.
+ */
+static inline void ptrace_release_task(struct task_struct *task)
+{
+        BUG_ON(!list_empty(&task->ptraced));
+        ptrace_unlink(task);
+        BUG_ON(!list_empty(&task->ptrace_entry));
+}
+
 #ifndef force_successful_syscall_return
 /*
  * System call handlers that, upon successful completion, need to return a