Re: [RESEND] [PATCH] VFS: make file->f_pos access atomic on 32bit arch

Pavel Machek
2008-10-09T12:33:43Z

On Tue 2008-10-07 20:59:23, Peter Zijlstra wrote:
> On Tue, 2008-10-07 at 10:50 -0700, Andrew Morton wrote:
> > On Wed, 8 Oct 2008 03:27:44 +1100 Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
> > > So.. is everyone agreed that corrupting f_pos is a bad thing? (serious
> > > question) If so, then we should get something like this merged sooner
> > > rather than later.
> >
> > - two threads/processes sharing the same fd
> >
> > - both appending the same fd
> >
> > - both hit the small race window right around the time when the file
> > flips over a multiple of 4G.
> >
> > 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.

Why is it outside spec?

> IMHO not worth fixing..

I believe we even have append-only flag, similar to immutable, which
is used for security...??

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