linux-kernel - Re: Yet another borken page_count() check in invalidate_inode

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Message-Id: <20061115112426.84e5417c.akpm@osdl.org>
Date:	Wed, 15 Nov 2006 11:24:26 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Trond Myklebust <Trond.Myklebust@...app.com>
Cc:	Charles Edward Lever <chucklever@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Yet another borken page_count() check in
 invalidate_inode_pages2()....

On Wed, 15 Nov 2006 13:05:13 -0500
Trond Myklebust <Trond.Myklebust@...app.com> wrote:

> On Wed, 2006-11-15 at 08:46 -0800, Andrew Morton wrote:
> 
> > but nobody could have started another writeback after the "..." because they
> > couldn't have got the lock_page(), and lock_page() is required for
> > ->writepage()?
> 
> Nothing can have called writepage(), but something may be calling
> ->writepages(). That may call set_page_writeback without taking the page
> lock.
> 

The protocol is

	lock_page()
	set_page_writeback()
	->writepage()

and there are various places which assume that nobody will start new
writeout of a locked page.  But I forget where they are - things have always
been this way.

If NFS is running set_page_writeback() against an unlocked page then I
don't know what will break.  I didn't know it was doing that.

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