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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Oleg Nesterov <oleg@redhat.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Wen Yang <wen.yang99@zte.com.cn>, majiang <ma.jiang@zte.com.cn>
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Date:   Fri, 20 Jul 2018 18:41:34 -0500
In-Reply-To: <20180717101811.GB27482@redhat.com> (Oleg Nesterov's message of
        "Tue, 17 Jul 2018 12:18:12 +0200")
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Subject: Re: [RFC][PATCH 07/11] signal: Deliver group signals via PIDTYPE_TGID not PIDTYPE_PID
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Oleg Nesterov <oleg@redhat.com> writes:

> On 07/17, Oleg Nesterov wrote:
>>
>> And, I didn't mention this yesterday, but probably the next 08/11 patch can
>> have the same problem. But this is a bit more complicated because send_sigio()
>> uses the same "type" both for do_each_pid_task() and as an argument passed to
>> do_send_sig_info().
>
> perhaps it can simply do
>
> 	if (type <= PIDTYPE_TGID) {
> 		rcu_read_lock();
> 		p = pid_task(pid, PIDTYPE_PID);
> 		send_sigio_to_task(p, fown, fd, band, type);
> 		rcu_read_unlock();
> 	} else {
> 		read_lock(&tasklist_lock);
> 		do_each_pid_task(pid, type, p) {
> 			send_sigio_to_task(p, fown, fd, band, type);
> 		} while_each_pid_task(pid, type, p);
> 		read_unlock(&tasklist_lock);
> 	}
>
> this way we also avoid tasklist_lock in F_OWNER_TID/F_OWNER_PID case.

I like that.  I updated that code in a different way but that looks
more elegant and I think I will incoporate it.

> To clarify, it is not that I think any sane application can do
> fcntl(F_OWNER_PID, thread_tid) but still this is a user-visible change
> we can easily avoid.

Agreed.

I do think 

Eric