linux-kernel - Re: [RESEND] [PATCH] VFS: make file->f

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Message-Id: <200810081335.44576.nickpiggin@yahoo.com.au>
Date:	Wed, 8 Oct 2008 13:35:44 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	torvalds@...ux-foundation.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Theodore Ts'o <tytso@....edu>
Subject: Re: [RESEND] [PATCH] VFS: make file->f_pos access atomic on 32bit arch

On Wednesday 08 October 2008 05:59, Peter Zijlstra wrote:
> On Tue, 2008-10-07 at 10:50 -0700, Andrew Morton wrote:

> > It's pretty damn improbable, and I think we can afford to spend the
> > time to get this right in 2.6.29.
>
> The whole point is that such usage is outside the specification and thus
> we don't strictly need to fix this.
>
> So the question Nick is asking is, do we want to slow down the kernel
> for a few broken user-space applications. Esp. since the race doesn't
> affect anybody else except the broken users of the file descriptor.

Right you are. That's the fundamental question. The actual details of
the fix and how likely the race is don't really matter until we
answer the first question (except to say that the "fix" is never going
to be free).

We've lasted this long with the current semantics. So the natural
reaction to anything that strengthens the semantics now is "why?". If
we do that then we can basically never return to the weaker semantics.
So there had better be a really good reason.
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