[PATCH] fix exec deadlock when ptrace used inside the thread group

If one thread uses ptrace on another thread in the same thread group, there
can be a deadlock when calling exec.  The ptrace_stop change ensures that
no tracing stop can be entered for a queued signal, or exit tracing, if the
tracer is part of the same dying group.  The exit_notify change prevents a
ptrace zombie from sticking around if its tracer is in the midst of a group
exit (which an exec fakes), so these zombies don't hold up de_thread's
synchronization.  The de_thread change ensures the new thread group leader
doesn't wind up ptracing itself, which would produce its own deadlocks.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 24f873e55080..8459791d6bc1 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -685,6 +685,14 @@ static inline int de_thread(struct task_struct *tsk)
 		 */
 		ptrace = leader->ptrace;
 		parent = leader->parent;
+		if (unlikely(ptrace) && unlikely(parent == current)) {
+			/*
+			 * Joker was ptracing his own group leader,
+			 * and now he wants to be his own parent!
+			 * We can't have that.
+			 */
+			ptrace = 0;
+		}
 
 		ptrace_unlink(current);
 		ptrace_unlink(leader);