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Date: Wed, 1 Jul 2015 17:47:43 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>, Benjamin LaHaise <bcrl@kvack.org>,
        Hugh Dickins <hughd@google.com>, Jeff Moyer <jmoyer@redhat.com>,
        Kirill Shutemov <kirill.shutemov@linux.intel.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/4] mremap: don't do mm_populate(new_addr) on failure
Message-ID: <20150701154743.GB14934@redhat.com>
References: <20150619231915.GA25884@redhat.com> <alpine.DEB.2.10.1506301533150.24266@chino.kir.corp.google.com>
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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.