Date: Mon, 8 Sep 2003 10:44:13 +0100
From: Jamie Lokier <jamie@shareable.org>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: Hugh Dickins <hugh@veritas.com>, Andrew Morton <akpm@osdl.org>,
       Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
       Linus Torvalds <torvalds@osdl.org>
Subject: Re: [PATCH] Alternate futex non-page-pinning and COW fix
Message-ID: <20030908094413.GB25176@mail.jlokier.co.uk>
References: <20030907132010.GB19977@mail.jlokier.co.uk> <20030908020812.4EC372C609@lists.samba.org>
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Rusty Russell wrote:
> In message <20030907132010.GB19977@mail.jlokier.co.uk> you write:
> > I don't see a problem, as long as it is documented.  Anybody grokking
> > the old futex code would expect futexes to move with mappings.
> 
> BTW, I don't know of anyone *doing* this, but IMHO it's not worth a
> single line of kernel code, since if you don't adjust your futex
> addresses when you mremap, the try_down_futex will segv after the poll
> or whatever.  As a programmer, I would *expect* to have to reset the
> futexes (along with every other pointer into the map) when mremap
> happens: after all, I told the kernel to watch the old address.  If it
> still works, great, but I'd not expect it.

Sure.  As long as it's documented, because my expectation is the
opposite of yours :)

(Some uses of futex don't read the memory after they are woken, until
they have re-tested some other condition and can recalculate the
address, so segv and pointers-into-the-map don't occur in these uses).

-- Jamie
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