Re: Please revert kobject_uevent UMH_NO_WAIT

[Will Newton <will.newton@gmail.com>]

On Thu, Apr 16, 2009 at 10:30 PM, Arjan van de Ven
<arjan@linux.intel.com> wrote:
> Greg KH wrote:
>>
>> 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@i-love.sakura.ne.jp>
>>> Signed-off-by: Hugh Dickins <hugh@veritas.com>
>>
>> Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
>
> Acked-by: Arjan van de Ven <arjan@linux.intel.com>
> as well
>
> not worth the hassle if this breaks too much

Acked-by: Will Newton <will.newton@gmail.com>

It's causing crashes for me too (reported 10 days ago).

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