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From: Christoph Hellwig <>
Cc:, Greg KH <>,, Andrew Morton <>,,
	Christoph Hellwig <>
Subject: Re: bio pages with zero page reference count
Date: Mon, 18 Dec 2006 22:53:43 +0000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Mon, Dec 18, 2006 at 05:21:09PM -0500, Ed L. Cashin wrote:
> (This email is a followup to "Re: [PATCH] fix aoe without
> scatter-gather [Bug 7662]".)
> On Mon, Dec 18, 2006 at 12:53:00PM -0500, Ed L. Cashin wrote:
> ...
> > This patch eliminates the offset data on cards that don't support
> > scatter-gather or have had scatter-gather turned off.  There remains
> > an unrelated issue that I'll address in a separate email.
> After fixing the problem with the skb headers, we noticed that there
> were still problems when scatter gather wasn't in use.  XFS was giving
> us bios that had pages with a reference count of zero.
> The aoe driver sets up the skb with the frags pointing to the pages,
> and when scatter gather isn't supported and __pskb_pull_tail gets
> involved, put_page is called after the data is copied from the pages.
> That causes problems because of the zero page reference count.
> It seems like it would always be incorrect for one part of the kernel
> to give pages with a zero reference count to another part of the
> kernel, so this seems like a bug in XFS.
> Christoph Hellwig, though, points out,
>   > It's a kmalloced page.  The same can happen with ext3 aswell, but
>   > only when doing log recovery.  The last time this came up (vs
>   > iscsi) the conclusion was that the driver needs to handle this
>   > case.
> In attempting to find the conversation he was referencing, I only
> found this:
>   Subject: tcp_sendpage and page allocation lifetime vs. iscsi
>   Date: 2005-04-25 17:02:59 GMT
> If anyone has a better reference, I'd like to see it.

I searched around a little bit and found these:

But that's not the conclusion I was looking for.  

  reply	other threads:[~2006-12-18 22:53 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
2006-12-18 17:53 ` [PATCH] fix aoe without scatter-gather [Bug 7662] Ed L. Cashin
2006-12-18 22:21   ` bio pages with zero page reference count Ed L. Cashin
2006-12-18 22:53     ` Christoph Hellwig [this message]
2007-01-19 16:21       ` Ed L. Cashin

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