linux-kernel - Re: + kmod-avoid-deadlock-by-recursive-kmod-call.patch added to -mm tree

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Message-ID: <87ipjxdfbg.fsf@rustcorp.com.au>
Date:	Fri, 27 Jan 2012 13:25:47 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Oleg Nesterov <oleg@...hat.com>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: + kmod-avoid-deadlock-by-recursive-kmod-call.patch added to -mm tree

On Thu, 26 Jan 2012 18:56:12 +0100, Oleg Nesterov <oleg@...hat.com> wrote:
> > @@ -449,6 +460,16 @@ int call_usermodehelper_exec(struct subp
> >  		retval = -EBUSY;
> >  		goto out;
> >  	}
> > +	/*
> > +	 * Worker thread must not wait for khelper thread at below
> > +	 * wait_for_completion() if the thread was created with CLONE_VFORK
> > +	 * flag, for khelper thread is already waiting for the thread at
> > +	 * wait_for_completion() in do_fork().
> > +	 */
> > +	if (wait != UMH_NO_WAIT && current == kmod_thread_locker) {
> > +		retval = -EBUSY;
> > +		goto out;
> > +	}
> 
> So, this is because khelper_wq's max_active == 1.
> 
> Can't we simply kill khelper_wq and use system_unbound_wq instead?

I'd prefer that, because then we'd hit the existing "too many modprobes"
check.

Thanks,
Rusty.
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