From: Rusty Russell <rusty@rustcorp.com.au>
To: Linus Torvalds <torvalds@osdl.org>
Cc: Jamie Lokier <jamie@shareable.org>,
Rusty Russell <rusty@rustcorp.com.au>,
Hugh Dickins <hugh@veritas.com>,
Ulrich Drepper <drepper@redhat.com>,
Andrew Morton <akpm@osdl.org>,
Stephen Hemminger <shemminger@osdl.org>,
Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Make futex waiters take an mm or inode reference
Date: Tue, 09 Sep 2003 14:02:15 +1000 [thread overview]
Message-ID: <20030909040403.B97352C0F0@lists.samba.org> (raw)
In-Reply-To: Your message of "Mon, 08 Sep 2003 11:52:07 MST." <Pine.LNX.4.44.0309081144390.3202-100000@home.osdl.org>
In message <Pine.LNX.4.44.0309081144390.3202-100000@home.osdl.org> you write:
> So is there any reason to really having "private.mm" AT ALL? From what I
> can tell, it is not actually ever used (all "mm" users are "current->mm"),
> so I don't see the point of incrementing a count for it either.
>
> Or did I miss something?
Yes. Firstly, you can't do "wake one" if the one you wake might be
some completely unrelated process which happens to use the same
address. Secondly, I implemented fair futexes by relying on the
return value of FUTEX_WAKE to indicate how many people were woken: you
set the futex to a magic value, call FUTEX_WAKE(1), and if it returns
1, you've "passed" the futex directly, otherwise you unlock the futex
like normal. This is surprisingly useful for implementing
"drop_futex_if_someone_is_waiting()" in cleanup threads etc.
Sorry,
Rusty.
--
Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
prev parent reply other threads:[~2003-09-09 4:04 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-09-08 18:20 [PATCH] Make futex waiters take an mm or inode reference Jamie Lokier
2003-09-08 18:34 ` Jamie Lokier
2003-09-08 18:52 ` Linus Torvalds
2003-09-08 20:00 ` Jamie Lokier
2003-09-09 4:02 ` Rusty Russell [this message]
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