linux-kernel - Re: CLONE_VM: parent terminates silently when child segfaults

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Message-ID: <20100204105017.GA21188@redhat.com>
Date:	Thu, 4 Feb 2010 11:50:17 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	Frank Heckenbach <f.heckenbach@...soft.de>,
	linux-kernel@...r.kernel.org
Subject: Re: CLONE_VM: parent terminates silently when child segfaults

On 02/04, Américo Wang wrote:
>
> On Thu, Jan 28, 2010 at 4:48 AM, Frank Heckenbach
> <f.heckenbach@...soft.de> wrote:
> > When a process cloned with CLONE_VM is killed by SIGSEGV, the parent
> > process is terminated silently.
>
> Becase SIGSEGV and SIGILL are coredump signals, when you use CLONE_VM,
> child process will share the memory space with its parent, what would
> you expect the parent behaves when its child coredumping their shared memory
> space?

Yes, exactly. The coredump signals kill/dump all threads which share
this ->mm, this is intentional.

As for status = 0 I agree, this looks strange. In fact I already
suggested the change below a long ago, but I don't remember why it
was declined (or probably it was unnoticed).

The patch below doesn't add 0x80 to ->group_exit_code in case we
really dumped the core, but at least the coredumping signal is
visible to do_wait/etc.

Oleg.

--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1550,6 +1550,7 @@ static int zap_process(struct task_struc
 	int nr = 0;
 
 	start->signal->flags = SIGNAL_GROUP_EXIT;
+	start->signal->group_exit_code = exit_code;
 	start->signal->group_stop_count = 0;
 
 	t = start;
@@ -1574,7 +1575,6 @@ static inline int zap_threads(struct tas
 	spin_lock_irq(&tsk->sighand->siglock);
 	if (!signal_group_exit(tsk->signal)) {
 		mm->core_state = core_state;
-		tsk->signal->group_exit_code = exit_code;
 		nr = zap_process(tsk);
 	}
 	spin_unlock_irq(&tsk->sighand->siglock);

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