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Date: Thu, 27 Mar 2014 16:46:57 +0800
From: David Xu <davidxu@freebsd.org>
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To: Mateusz Guzik <mjguzik@gmail.com>
Subject: Re: svn commit: r263755 - head/sys/kern
References: <201403252330.s2PNUaei052956@svn.freebsd.org>
 <5333D70D.7050306@freebsd.org> <20140327083730.GA22942@dft-labs.eu>
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Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org,
 src-committers@freebsd.org, Mateusz Guzik <mjg@FreeBSD.org>
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On 2014/03/27 16:37, Mateusz Guzik wrote:
> On Thu, Mar 27, 2014 at 03:45:17PM +0800, David Xu wrote:
>> I think the async process pointer can be cleared when a process exits
>> by registering an event handler. please see attached patch.
>>
>
> Sure, but I'm not very fond of this solution.
>
> This is a rather obscure bug you wont hit unless you explicitly try,
> and even then you need root privs by default.
>
OK, but I don't like the bug exists in kernel. It is not obscure for me,
I can run "shutdown now" command, and insert a device, and then the
kernel will write garbage data into freed memory space.

> As such writing a callback function which will be executed for all exiting
> processes seems unjustified for me.
>
> Ideally we would get some mechanism which would allow to register
> callbacks for events related to given entity. Then it could be used to
> provide a "call this function when process p exits", amongst other things.
>

Yes, but the callback itself is cheap enough and is not worth to be
per-entity entry.