netdev - Re: SG_IO with >4k buffer size to iscsi sg device causes "Bad page" panic

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Date:	Fri, 08 Jun 2007 16:22:12 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Yanling.Qi@....com (Qi, Yanling)
Cc:	open-iscsi@...glegroups.com, netdev@...r.kernel.org,
	linux-scsi@...r.kernel.org,
	linux-iscsi-devel@...ts.sourceforge.net, michaelc@...wisc.edu,
	dougg@...que.net, James.Bottomley@...eleye.com
Subject: Re: SG_IO with >4k buffer size to iscsi sg device causes "Bad page" panic

Please don't drop CCs.

Qi, Yanling <Yanling.Qi@....com> wrote:
>
>> Qi, Yanling <Yanling.Qi@....com> wrote:
>> > @@ -2571,6 +2572,13 @@ sg_page_malloc(int rqSz, int lowDma, int
>> >                resp = (char *) __get_free_pages(page_mask, order);
>> > /* try half */
>> >                resSz = a_size;
>> >        }
>> > +       tmppage = virt_to_page(resp);
>> > +       for( m = PAGE_SIZE; m < resSz; m += PAGE_SIZE )
>> > +       {
>> > +               tmppage++;
>> > +               SetPageReserved(tmppage);
>> > +       }
>> > +
>> 
> [Qi, Yanling]
> If I do a get_page() at sg_page_malloc() time and then do a put_page()
> at sg_page_free() time, I worry about a race condition that the page
> gets re-used before calling free_pages().

Could you explain what is going to cause this page to be reused if it
has a non-zero reference count?

Thanks,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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