linux-kernel - Re: Please revert kobject_uevent UMH_NO

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Date:	Thu, 16 Apr 2009 14:24:36 -0700
From:	Greg KH <gregkh@...e.de>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	arjan@...ux.intel.com, alan@...rguk.ukuu.org.uk,
	viro@...IV.linux.org.uk, jmorris@...ei.org,
	akpm@...ux-foundation.org, paulmck@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: Please revert kobject_uevent UMH_NO_WAIT

On Thu, Apr 16, 2009 at 09:55:29PM +0100, Hugh Dickins wrote:
> Please revert commit f520360d93cdc37de5d972dac4bf3bdef6a7f6a7
> "kobject: don't block for each kobject_uevent".
> 
> Tetsuo Handa, running a kernel with CONFIG_DEBUG_PAGEALLOC=y
> and CONFIG_UEVENT_HELPER_PATH=/sbin/hotplug, has been hitting RCU
> detected CPU stalls: it's been spinning in the loop where do_execve()
> counts up the args (but why wasn't fixup_exception working? dunno).
> 
> The recent change, switching kobject_uevent_env() from UMH_WAIT_EXEC
> to UMH_NO_WAIT, is broken: the exec uses args on the local stack here,
> and an env which is kfreed as soon as call_usermodehelper() returns.
> It very much needs to wait for the exec to be done.
> 
> Or keep the UMH_NO_WAIT, and complicate the code to allocate and free
> these resources correctly?  No, as GregKH pointed out when making the
> commit, CONFIG_UEVENT_HELPER_PATH="" is a much better optimization -
> though some distros are still saying /sbin/hotplug in their .config,
> yet with no such binary in their initrd or their root.
> 
> Or...
> 
> [PATCH] revert kobject_uevent UMH_NO_WAIT
> 
> Reported-by: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
> Signed-off-by: Hugh Dickins <hugh@...itas.com>

Acked-by: Greg Kroah-Hartman <gregkh@...e.de>

Linus, I can do this in a tree of patches to send to you or you can do it
yourself, which ever is easier.

thanks,

greg k-h
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