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Date:   Mon, 30 Sep 2019 09:44:37 +0200
From:   Heiko Carstens <heiko.carstens@de.ibm.com>
To:     Qian Cai <cai@lca.pw>, Peter Oberparleiter <oberpar@linux.ibm.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, gor@linux.ibm.com,
        borntraeger@de.ibm.com, linux-s390@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/page_alloc: fix a crash in free_pages_prepare()
References: <1569613623-16820-1-git-send-email-cai@lca.pw>
 <20190927134859.95a2f4908bdcea30df0184ed@linux-foundation.org>
 <1569618908.5576.240.camel@lca.pw>
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On Fri, Sep 27, 2019 at 05:15:08PM -0400, Qian Cai wrote:
> On Fri, 2019-09-27 at 13:48 -0700, Andrew Morton wrote:
> > On Fri, 27 Sep 2019 15:47:03 -0400 Qian Cai <cai@lca.pw> wrote:
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -1175,11 +1175,11 @@ static __always_inline bool free_pages_prepare(struct page *page,
> > >  		debug_check_no_obj_freed(page_address(page),
> > >  					   PAGE_SIZE << order);
> > >  	}
> > > -	arch_free_page(page, order);
> > >  	if (want_init_on_free())
> > >  		kernel_init_free_pages(page, 1 << order);
> > >  
> > >  	kernel_poison_pages(page, 1 << order, 0);
> > > +	arch_free_page(page, order);
> > >  	if (debug_pagealloc_enabled())
> > >  		kernel_map_pages(page, 1 << order, 0);
> > 
> > This is all fairly mature code, isn't it?  What happened to make this
> > problem pop up now?
> 
> In the past, there is only kernel_poison_pages() would trigger it but it needs
> "page_poison=on" kernel cmdline, and I suspect nobody tested that on s390 in the
> past.

Yes. Peter Oberparleiter reported this also before my short vacation,
but I didn't have time to look into this. Thanks for fixing!

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>