linux-kernel - Time window between process dying and its proc directory going way

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Date:	Fri, 8 Apr 2011 19:55:42 -0700
From:	Pengcheng <pengcheng.chen@....org>
To:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Time window between process dying and its proc directory going way

Dear folks,

I'm experimenting 2.6.3x kernel on some network test boxes. Under very
heavy network traffic, the proc directory of a process *seems* not
going away within a short time window  after the process dies.

In our system, we have a daemon launching many processes, a watchdog
monitoring  heartbeats of each process. If  a process stopped
heartbeat for a while, the daemon will get a request from watchdog to
kill the process and restart it.

To kill a process, we send a SIGQUIT for it to exit gracefully. If it
is still around after 10 seconds, we send a SIGKILL. We waitpid(-1,
WNOHANG) before trying to start a new process.

We found a problem in our testing: after a process was killed,  its
/proc/<pid> directory (*we suspect*) might still be there for a while
(at least 4 seconds) and we could still read files in it.

Any thoughts on how to reproduce this problem easily (without heavy
networking traffic)?

Thanks in advance!
Pengcheng
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