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From:   Florian Weimer <fweimer@redhat.com>
To:     cambda@linux.alibaba.com
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
        Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
        Dust Li <dust.li@linux.alibaba.com>,
        Tony Lu <tonylu@linux.alibaba.com>
Subject: Re: Syscall kill() can send signal to thread ID
References: <69E17223-F0CA-4A4C-AAD7-065D6E6266D9@linux.alibaba.com>
        <87pmfn5tu1.fsf@email.froward.int.ebiederm.org>
        <87r102ejwo.fsf@oldenburg.str.redhat.com>
        <0CC7D0E7-71C5-4DAC-8A01-F9E13659F864@linux.alibaba.com>
Date:   Fri, 23 Sep 2022 09:53:30 +0200
In-Reply-To: <0CC7D0E7-71C5-4DAC-8A01-F9E13659F864@linux.alibaba.com>
        (cambda@linux.alibaba.com's message of "Fri, 23 Sep 2022 14:25:05
        +0800")
Message-ID: <87illeedc5.fsf@oldenburg.str.redhat.com>
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> I don't quite understand what you mean, sorry. But if kill() returns
> -ESRCH for tid which is not equal to tgid, kill() can only send signal
> to thread group via main thread id, that is what BSD did and manual
> said. It seems not odd?

It's still odd because there's one TID per process that's valid for
kill by accident.  That's all.

Thanks,
Florian