linux-kernel - Re: [PATCH 2/4] mremap: don't do mm_populate(new

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Message-ID: <20150701154743.GB14934@redhat.com>
Date:	Wed, 1 Jul 2015 17:47:43 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Hugh Dickins <hughd@...gle.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] mremap: don't do mm_populate(new_addr) on failure

On 06/30, David Rientjes wrote:
>
> On Sat, 20 Jun 2015, Oleg Nesterov wrote:
>
> > --- a/mm/mremap.c
> > +++ b/mm/mremap.c
> > @@ -574,8 +574,10 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
> >  		ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
> >  	}
> >  out:
> > -	if (ret & ~PAGE_MASK)
> > +	if (ret & ~PAGE_MASK) {
> >  		vm_unacct_memory(charged);
> > +		locked = 0;
> > +	}
> >  	up_write(&current->mm->mmap_sem);
> >  	if (locked && new_len > old_len)
> >  		mm_populate(new_addr + old_len, new_len - old_len);
>
> Perhaps I'm looking at the wrong tree (next-20150630), but why does
> setting locked to 0 here matter if it's unreferenced?

See the "if (locked && ...)" check before mm_populate(). We should
not do this if move_vma() fails.

Oleg.

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