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Date:   Tue, 17 Jul 2018 12:18:12 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     "Eric W. Biederman" <ebiederm@xmission.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>
Subject: Re: [RFC][PATCH 07/11] signal: Deliver group signals via
 PIDTYPE_TGID not PIDTYPE_PID
Message-ID: <20180717101811.GB27482@redhat.com>
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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.

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.

Oleg.