linux-kernel - Re: [PATCH] aio: propogate post-EIOCBQUEUED errors to completion event

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Date:	Tue, 20 Feb 2007 19:05:19 -0500
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Zach Brown <zach.brown@...cle.com>
Cc:	Chris Mason <chris.mason@...cle.com>,
	Benjamin LaHaise <bcrl@...ck.org>,
	"Ananiev, Leonid I" <leonid.i.ananiev@...el.com>,
	linux-aio@...ck.org, linux-kernel@...r.kernel.org,
	Suparna bhattacharya <suparna@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] aio: propogate post-EIOCBQUEUED errors to completion
	event

On Tue, 2007-02-20 at 10:40 -0800, Zach Brown wrote:
> >> There are some strange O_DIRECT corner cases in here such that the  
> >> 'last
> >> writer' may actually be a 'last reader' and winning can mean have  
> >> a copy
> >> of the page in page cache older than the copy on disk.
> >
> > As long as it is marked dirty so that it eventually gets synced to  
> > disk,
> > it shouldn't matter.
> 
> No, Chris is pointing out that an an O_DIRECT write can leave clean  
> read pages in the page cache.
>
> All it takes is giving a source buffer for the write which is an mmap 
> ()ed apeture of the region that is being written to.  If you get the  
> offsets right you can get the get_user_pages() down in fs/direct-io.c  
> will populate the page cache before the actual O_DIRECT write gets to  
> it.


With invalidate_inode_pages2()? That is supposed to wait until the page
lock is taken -> read is done. It then calls unmap_mapping_range() which
will remove the offending page from any existing mappings. Sure an
application could get stale data, but if it is reading while an O_DIRECT
write is proceeding, then it gets what it deserves.

Trond

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