linux-kernel - Re: [rfc patch 3/4] splice: remove confirm from pipe_buf

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Message-Id: <E1KBEmA-0002m2-EF@pomaz-ex.szeredi.hu>
Date:	Tue, 24 Jun 2008 22:06:02 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	torvalds@...ux-foundation.org
CC:	miklos@...redi.hu, jens.axboe@...cle.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [rfc patch 3/4] splice: remove confirm from
 pipe_buf_operations

> > 
> > Or it can only happen if there was an I/O error on reading the page.
> 
> Now, IO errors are something else. They should have the PG_error bit set, 
> and we should just return EIO or something.

Linus, you're right (as always), but see where this is going?  A rare
problem (splice() returning short count because of an invalidated
page) is becoming an even more rare problem (splice() returning
rubbish instead of an error, if ->readpage() failed, and filesystem
forgot to set PG_error).  And it won't show up in any other paths,
because the generic_file_aio_read() path will just check
PageUptodate(), and return -EIO if not.

OK, maybe we should add a WARN_ON(!PageError()) for the
!PageUptodate() case in generic_file_aio_read(), but that could still
leave some filesystems broken for a long time which experience I/O
errors rarely.

So I think the only sane solution here is to remove
ClearPageUptodate().  But that's a VM people's call, I don't have
enough insight into that.

Miklos
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