linux-kernel - Re: [resend][PATCH 4/4] oom: don't ignore rss in nascent mm

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Message-Id: <20101130085254.82CF.A69D9226@jp.fujitsu.com>
Date:	Tue, 30 Nov 2010 09:06:32 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, pageexec@...email.hu,
	Solar Designer <solar@...nwall.com>,
	Eugene Teo <eteo@...hat.com>,
	Brad Spengler <spender@...ecurity.net>,
	Roland McGrath <roland@...hat.com>
Subject: Re: [resend][PATCH 4/4] oom: don't ignore rss in nascent mm

> On 11/29, KOSAKI Motohiro wrote:
> >
> > > The patch is not complete, compat_copy_strings() needs changes.
> > > But, shouldn't it use get_arg_page() too? Otherwise, where do
> > > we check RLIMIT_STACK?
> >
> > Because NOMMU doesn't have variable length argv. Instead it is still
> > using MAX_ARG_STRLEN as old MMU code.
> >
> > 32 pages hard coded argv limitation naturally prevent this nascent mm
> > issue.
> 
> Ah, I didn't mean NOMMU. I meant compat_execve()->compat_copy_strings().
> If a 32bit process execs we seem to miss the RLIMIT_STACK check, no?

Ah, yes. that's bug. You have found more serious issue ;)



> > > The patch asks for the cleanups. In particular, I think exec_mmap()
> > > should accept bprm, not mm. But I'd prefer to do this later.
> > >
> > > Oleg.
> >
> > General request. Please consider to keep Brad's reported-by tag.
> 
> Yes, yes, sure.
> 
> > > +static void acct_arg_size(struct linux_binprm *bprm, unsigned long pages)
> 
> OK.
> 
> > Please move this function into #ifdef CONFIG_MMU. nommu code doesn't use it.
> 
> Well it does, to revert the MM_ANONPAGES counter. I'll add the empty
> function for NOMMU.
> 
> > > +{
> > > +	struct mm_struct *mm = current->mm;
> > > +	long diff = pages - bprm->vma_pages;
> >
> > I prefer to cast signed before assignment. It's safer more.
> 
> OK.
> 
> > > @@ -1003,6 +1024,7 @@ int flush_old_exec(struct linux_binprm *
> > >  	/*
> > >  	 * Release all of the old mmap stuff
> > >  	 */
> > > +	acct_arg_size(bprm, 0);
> >
> > Why do we need this unacct here? I mean 1) if exec_mmap() is success,
> > we don't need unaccount at all
> 
> Yes, we already killed all sub-threads. But this doesn't mean nobody
> else can use current->mm, think about CLONE_VM. The simplest example
> is vfork().

Right you are.


> > 2) if exec_mmap() is failure, an epilogue of
> > do_execve() does unaccount thing.
> 
> Yes.
> 
> Thanks Kosaki!
> 
> I'll resend v2 today. I am still not sure about compat_copy_strings()...
> 
> Oleg.
> 



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