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

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Date:	Mon, 30 Jan 2012 14:03:35 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: + kmod-avoid-deadlock-by-recursive-kmod-call.patch added to
	-mm tree

On 01/29, Tejun Heo wrote:
>
> BTW, why does it have to be unbound_wq?

Perhaps we can use another system_wq, but afaics WQ_UNBOUND makes sense
in this case. I mean, there is no reason to bind this work to any CPU.
See also below.

> Is it expected consume large
> amount of CPU cycles?

Currently __call_usermodehelper() does kernel_thread(), this is almost
all. But it can block waiting for kernel_execve().

Not sure this really makes sense, but if we kill khelper_wq perhaps we
can simplify this code a bit. We can change __call_usermodehelper()

		if (wait == UMH_WAIT_PROC)
	-		pid = kernel_thread(wait_for_helper, sub_info,
	-				    CLONE_FS | CLONE_FILES | SIGCHLD);
	+		wait_for_helper(...);
		else

IOW, the worker thread itself can do the UMH_WAIT_PROC work. This makes
this work really "long running", but then we can kill sub_info->complete
and use flush_work().

Oleg.

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