linux-kernel - Re: [2.6.30-rc1] RCU detected CPU 1 stall

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Date:	Thu, 16 Apr 2009 06:15:13 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
cc:	arjan@...ux.intel.com, gregkh@...e.de, 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: [2.6.30-rc1] RCU detected CPU 1 stall

On Thu, 16 Apr 2009, Tetsuo Handa wrote:
> Indeed, we can't use "argv" put on stack memory if we use "no wait" mode.
> We need to ensure that memory region pointed by "argv" is valid until
> do_execve() finishes. However,
> | 
> | exit:
> | 	kfree(devpath);
> | 	kfree(env);
> | 	return retval;
> | }
> "env" can be overwritten as well as "argv".
> We need to ensure that memory region pointed by "env" is valid until
> do_execve() finishes, don't we?
> 
> I think we need to use UMH_WAIT_EXEC instead of UMH_NO_WAIT.

Yes, of course you're right, silly me.

It could be worked around using call_usermodehelper_setcleanup()
to arrange for the freeing there instead of here in this case;
but if CONFIG_UEVENT_HELPER_PATH="" is the better answer anyway,
let's not waste any more time on this, just revert the broken patch
(which is what simply changing UMH_NO_WAIT to UMH_WAIT_EXEC does).

I'd hoped to get confirmation that the mmap.c part of the patch
was all the extra needed; but never mind, that's clearly good.

Thanks a lot: I'll send in a revert request,
and the acct_stack_growth patch, later today.

Hugh
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