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From:   Florian Weimer <fweimer@redhat.com>
To:     =?utf-8?Q?J=C3=BCrg?= Billeter <j@bitron.ch>
Cc:     Christian Brauner <christian@brauner.io>,
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        timmurray@google.com, linux-man@vger.kernel.org,
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Subject: Re: [PATCH v4] signal: add taskfd_send_signal() syscall
References: <20181206121858.12215-1-christian@brauner.io>
        <87h8fq7s84.fsf@oldenburg2.str.redhat.com>
        <b0e946bcac12358841c9a99017da819b00794d9c.camel@bitron.ch>
Date:   Thu, 06 Dec 2018 14:12:41 +0100
In-Reply-To: <b0e946bcac12358841c9a99017da819b00794d9c.camel@bitron.ch>
 (=?utf-8?Q?=22J=C3=BCrg?=
        Billeter"'s message of "Thu, 06 Dec 2018 13:45:39 +0100")
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* Jürg Billeter:

> On Thu, 2018-12-06 at 13:30 +0100, Florian Weimer wrote:
>> * Christian Brauner:
>> 
>> > /* zombies */
>> > Zombies can be signaled just as any other process. No special error will be
>> > reported since a zombie state is an unreliable state (cf. [3]).
>> 
>> I still disagree with this analysis.  If I know that the target process
>> is still alive, and it is not, this is a persistent error condition
>> which can be reliably reported.  Given that someone might send SIGKILL
>> to the process behind my back, detecting this error condition could be
>> useful.
>
> As I understand it, kill() behaves the same way. I think it's good that
> this new syscall keeps the behavior as close as possible to kill().

No, kill does not behave in this way because the PID can be reused.
The error condition is not stable there.

Thanks,
Florian