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

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Message-Id: <201202042156.HCJ57836.OQMFSVJHLtFOFO@I-love.SAKURA.ne.jp>
Date:	Sat, 4 Feb 2012 21:56:49 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	oleg@...hat.com, tj@...nel.org
Cc:	rusty@...tcorp.com.au, akpm@...ux-foundation.org,
	arjan@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: + kmod-avoid-deadlock-by-recursive-kmod-call.patch added to-mm tree

Oleg Nesterov wrote:
> What do you think about s/khelper/system/ instead of this patch?

I'm not catching up with this topic. But I'm fine with any solution provided
that it can handle

  some kernel function calls request_module()

    request_module() triggers call_usermodehelper("/sbin/modprobe", UMH_WAIT_PROC)

      /sbin/modprobe loads a kernel module

        loading a kernel module triggers kobject_uevent_env()

          kobject_uevent_env() calls call_usermodehelper("/sbin/hotplug", UMH_WAIT_EXEC)

            do_execve("/sbin/hotplug") calls request_module("binfmt-0000")

              request_module("binfmt-0000") triggers call_usermodehelper("/sbin/modprobe", UMH_WAIT_PROC)

                /sbin/modprobe fails to load binfmt-0000 module

call trace on an UP machine.

kmod-avoid-deadlock-by-recursive-kmod-call.patch is for avoiding
call_usermodehelper("/sbin/modprobe", UMH_WAIT_PROC) called from
call_usermodehelper("/sbin/hotplug", UMH_WAIT_EXEC).
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