linux-kernel - Re: [PATCH 0/3] aio: ctx->dead cleanups

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Date:	Thu, 18 Jun 2015 18:08:29 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Jeff Moyer <jmoyer@...hat.com>, linux-aio@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] aio: ctx->dead cleanups

On 06/17, Oleg Nesterov wrote:
>
> On 06/17, Al Viro wrote:
> >
> > On Wed, Jun 17, 2015 at 01:39:06AM +0100, Al Viro wrote:
> >
> > And yes, the leak you've spotted is real, but I would very much prefer
> > to avoid that goto - something like this instead:
> >
> > diff --git a/mm/mremap.c b/mm/mremap.c
> > index 034e2d3..b36b530 100644
> > --- a/mm/mremap.c
> > +++ b/mm/mremap.c
> > @@ -291,7 +291,10 @@ static unsigned long move_vma(struct vm_area_struct *vma,
> >  		if (err < 0) {
> >  			move_page_tables(new_vma, new_addr, vma, old_addr,
> >  					 moved_len, true);
> > -			return err;
> > +			vma = new_vma;
> > +			old_len = new_len;
> > +			old_addr = new_addr;
> > +			new_addr = err;
>
> Personally, I'd really prefer to factor out at least this
> move_page_tables() with six args. Although I agree, "goto previous_if"
> doesn't look nice too, this needs cleanup.
>
> But this is minor. I am already sleeping, most probably I misread
> this code. But it seems that there is another bug with VM_ACCOUNT.
>
> I'll recheck tomorrow and write another email.

Yes this look wrong. At least we shouldn't set *locked on failure.
mm->locked_vm += new_len is probably fine, but doesn't look really
nice because ->locked_vm can underflow in do_munmap() before that.

I'll send the fixes, but also I'll try to cleanup this code. Not
sure I will succeed ;)

Oleg.

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