linux-kernel - Re: [PATCH] [8/18] BKL-removal: Remove BKL from remote

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Date:	Mon, 28 Jan 2008 14:27:35 +0100
From:	Andi Kleen <ak@...e.de>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Steve French <smfrench@...il.com>, swhiteho@...hat.com,
	sfrench@...ba.org, vandrove@...cvut.cz,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] [8/18] BKL-removal: Remove BKL from remote_llseek

On Monday 28 January 2008 13:56:05 Alan Cox wrote:
> > > No specific spec, just general quality of implementation.
> > 
> > I completely agree.  If one thread writes A and another writes B then the
> > kernel should record either A or B, not ((A & 0xffffffff00000000) | (B &
> > 0xffffffff))
> 
> Agree entirely: the spec doesn't allow for random scribbling in the wrong
> place. It doesn't cover which goes first or who "wins" the race but
> provides pwrite/pread for that situation. Writing somewhere unrelated is
> definitely not to spec 

Actually it would probably -- i guess it's undefined and in undefined
country such things can happen.

Also to be fair I think it's only a problem for the 4GB wrapping case
which is presumably rare (otherwise we would have heard about it)

Also worse really fixing it would be a major change to the VFS 
because of the way ->read/write are defined :/

-Andi
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