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Subject[PATCH] exit.c: call proc_exit_connector() after exit_state is set
From: Guillaume Morin <guillaume@morinfr.org>

The process events connector delivers a notification when a process
exits. This is really convenient for a process that spawns and wants
to monitor its children through an epoll-able() interface.

Unfortunately, there is a small window between when the event is
delivered and the child become wait()-able.

This is creates a race if the parent wants to make sure that it knows
about the exit, e.g

pid_t pid = fork();
if (pid > 0) {
register_interest_for_pid(pid);
if (waitpid(pid, NULL, WNOHANG) > 0)
{
/* We might have raced with exit() */
}
return;
}

/* Child */
execve(...)

register_interest_for_pid() would be telling the the connector socket
reader to pay attention to events related to pid.

Though this is not a bug, I think it would make the connector a bit
more usable if this race was closed by simply moving the call to
proc_exit_connector() from just before exit_notify() to right after.

Signed-off-by: Guillaume Morin <guillaume@morinfr.org>
Cc: matt.helsley@gmail.com
---
diff --git a/kernel/exit.c b/kernel/exit.c
index 1e77fc6..9b0ac8c 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -804,7 +804,6 @@ void do_exit(long code)

module_put(task_thread_info(tsk)->exec_domain->module);

- proc_exit_connector(tsk);

/*
* FIXME: do that only when needed, using sched_exit tracepoint
@@ -812,6 +811,7 @@ void do_exit(long code)
flush_ptrace_hw_breakpoint(tsk);

exit_notify(tsk, group_dead);
+ proc_exit_connector(tsk);
#ifdef CONFIG_NUMA
task_lock(tsk);
mpol_put(tsk->mempolicy);


--
Guillaume Morin <guillaume@morinfr.org>


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