Change ptrace_attach_task() to re-use the self-detaching engine first,
then do utrace_attach_task(UTRACE_ATTACH_CREATE).
Unlike the previous version, ptrace_attach_task() just calls
ptrace_lookup_engine() and changes context->resume. The only caller
which can find the self-attaching engine is ptrace_atttach(), we
can rely on ->cred_guard_mutex.
Todo: re-check this all and cleanup the mess in ptrace_attach_task().
But first I'd like to know if you agree with this approach.
---
kernel/ptrace.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
--- PU/kernel/ptrace.c~81_REUSE_DETACHING_ENGINE 2009-10-10
17:10:07.000000000 +0200
+++ PU/kernel/ptrace.c 2009-10-10 17:13:37.000000000 +0200
@@ -442,6 +442,22 @@ static int ptrace_attach_task(struct tas
struct utrace_engine *engine;
int err;
+ engine = ptrace_lookup_engine(tracee);
+ if (!IS_ERR(engine)) {
+ context = ptrace_context(engine);
+ if (context->resume == UTRACE_DETACH) {
+ /* we rely on ->cred_guard_mutex */
+ context->resume = UTRACE_RESUME;
+ /*
+ * Make sure we don't race with ptrace_report_signal()
+ */
+ utrace_barrier(tracee, engine);
+ if (engine->ops == &ptrace_utrace_ops)
+ goto finish;
+ }
+ utrace_engine_put(engine);
+ }
+
context = kzalloc(sizeof(*context), GFP_KERNEL);
if (unlikely(!context))
return -ENOMEM;
@@ -459,6 +475,7 @@ static int ptrace_attach_task(struct tas
kfree(context);
return err;
}
+finish:
/*
* It can fail only if the tracee is dead, the caller
* must notice this before setting PT_PTRACED.
