linux-kernel - [PATCH 0/3] exec_id/exit

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Date:	Mon, 19 Mar 2012 17:02:49 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Al Viro <viro@...iv.linux.org.uk>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	James Morris <james.l.morris@...cle.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Roland McGrath <roland@...k.frob.com>,
	Solar Designer <solar@...nwall.com>,
	Djalal Harouni <tixxdz@...ndz.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 0/3] exec_id/exit_signal fixes

Andrew, these changes are orthogonal to
"CLONE_PARENT shouldn't allow to set ->exit_signal" in -mm.

Please review/comment. The patches are really simple I hope,
but with or without them I do not understand eligible_child().

	/* Wait for all children (clone and not) if __WALL is set;
	 * otherwise, wait for clone children *only* if __WCLONE is
	 * set; otherwise, wait for non-clone children *only*.  (Note:
	 * A "clone" child here is one that reports to its parent
	 * using a signal other than SIGCHLD.) */
	if (((p->exit_signal != SIGCHLD) ^ !!(wo->wo_flags & __WCLONE))
	    && !(wo->wo_flags & __WALL))
		return 0;

OK, but exec/exit can change ->exit_signal "in between".

For example. The parent clones the !SIGCHLD child and does
do_wait(__WCLONE). The child execs. The parent still sleeps until
child exits but do_wait() returns ECHILD. And more, this also
depends on who does exec in mt case.

Or the parent execs. In this case eligible_child() depends on when
the child exits, before or after exec.

Anyway, the current check in exit_notify() is wrong, 2/2 tries to
fix this. But both patches add the (hopefully minor) user-visible
changes wrt eligible_child().

Really, I think de_thread() should set ->exit_signal = SIGCHLD for
each child. This looks simple and understandable, and with the
CLONE_PARENT change above we can kill self_exec_id/parent_exec_id.

May be de_thread() should also do __wake_up_parent() if it changes
->exit_signal. Or perhaps we should change eligible_child() to check
p->cloned_with_not_SIGCHLD. I dunno. I hope this doesn't matter
and nobody cares.

OTOH, I never understood why we should reset ->exit_signal if the
child execs but the parent is still the same.

3/3 is offtopic minor cleanup. Imho setmax_mm_hiwater_rss() in
de_thread() looks strange.

Oleg.

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