linux-kernel - Re: [RFC][PATCH 07/11] signal: Deliver group signals via PIDTYPE_TGID not PIDTYPE

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Message-ID: <20180717095628.GA27482@redhat.com>
Date:   Tue, 17 Jul 2018 11:56:28 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Wen Yang <wen.yang99@....com.cn>, majiang <ma.jiang@....com.cn>
Subject: Re: [RFC][PATCH 07/11] signal: Deliver group signals via
 PIDTYPE_TGID not PIDTYPE_PID

On 07/16, Eric W. Biederman wrote:
>
> There are two questions.
> a) Can we use the pid of a thread to find the thread group?
> b) Will the signal be queued in the thread group?

IMO "yes" to both questions, I simply see no reason to change the current
semantics. Even if glibc doesn't show the tread id's a user can see them
in /proc/$tgid/task/. So I think kill_pid_info() should just do

	p = pid_task(pid, PIDTYPE_PID);
	group_send_sig_info(p, PIDTYPE_TGID);

again, posix_timer_event() looks fine, but to me

	pid_task(timr->it_pid, shared ? PIDTYPE_TGID : PIDTYPE_PID)

looks like unnecessary complication,

	pid_task(timr->it_pid, PIDTYPE_PID);

should do the same thing.

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().

Oleg.