linux-kernel - Re: Possible bug introduced in commit 9b84cca

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Message-ID: <20120103142941.GA25488@redhat.com>
Date:	Tue, 3 Jan 2012 15:29:41 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	Tejun Heo <tj@...nel.org>, Denys Vlasenko <dvlasenk@...hat.com>,
	linux-kernel@...r.kernel.org,
	Łukasz Michalik <lmi@....uni.wroc.pl>,
	"Dmitry V. Levin" <ldv@...linux.org>
Subject: Re: Possible bug introduced in commit 9b84cca

On 12/29, Oleg Nesterov wrote:
>
> On 12/29, Oleg Nesterov wrote:
> >
> > On 12/28, Denys Vlasenko wrote:
> > >
> > > 931   clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0xf763dbd8) = 1048
> > > 1048  exit_group(42)                    = ?
> > > 931   waitpid(1048,  <unfinished ...>
> > > 1048  +++ exited with 42 +++
> > > 931   <... waitpid resumed> 0xf763d3a0, 0) = -1 ECHILD (No child processes)
> >
> I've made the simple test-case, it triggers the bug.

I am going to send the hack^Wpatch below to Linus as a temporary
workaround for 3.2.

Any chance you can test it?

I did the testing too with my test-case, but it would be nice to
know if it works for you.

Thanks,

Oleg.

--- x/kernel/exit.c~	2011-11-22 18:46:22.000000000 +0100
+++ x/kernel/exit.c	2012-01-03 14:37:17.000000000 +0100
@@ -1540,8 +1540,11 @@ static int wait_consider_task(struct wai
 	}
 
 	/* dead body doesn't have much to contribute */
-	if (p->exit_state == EXIT_DEAD)
+	if (unlikely(p->exit_state == EXIT_DEAD)) {
+		if (likely(!ptrace) && unlikely(ptrace_reparented(p)))
+			wo->notask_error = 0;
 		return 0;
+	}
 
 	/* slay zombie? */
 	if (p->exit_state == EXIT_ZOMBIE) {

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