From: torvalds@transmeta.com (Linus Torvalds)
To: linux-kernel@vger.kernel.org
Subject: Re: [Linux-ia64] reader-writer livelock problem
Date: Fri, 8 Nov 2002 17:57:13 +0000 (UTC) [thread overview]
Message-ID: <aqgttp$2qf$1@penguin.transmeta.com> (raw)
In-Reply-To: 1036777105.13021.13.camel@ixodes.goop.org
In article <1036777105.13021.13.camel@ixodes.goop.org>,
Jeremy Fitzhardinge <jeremy@goop.org> wrote:
>
>Even without interrupts that would be a bug. It isn't ever safe to
>attempt to retake a read lock if you already hold it, because you may
>deadlock with a pending writer. Fair multi-reader locks aren't
>recursive locks.
.. but I don't think we have any real users who use them for recursion,
so the only "recursion" right now is through interrupts that use this
feature.
(At least that was true a long time time ago, maybe we've added truly
recursive users since)
>> Actually, giving this som emore thought, I really suspect that the
>> simplest solution is to alloc a separate "fair_read_lock()", and paths
>> that need to care about fairness (and know they don't have the irq
>> issue)
>> can use that, slowly porting users over one by one...
>
>Do you mean have a separate lock type, or have two different read_lock
>operations on the current type?
That depends on whether it is even sanely implementable to share the
same lock. It may not be.
>From a migration standpoint it would be easiest (by far) to be able to
share the lock type and to mix operations (ie an interrupt - or
recursive user - could just use the non-fair version, while others could
use the fair version on the same lock). However, I have this nagging
suspicion that it might be a total nightmare to implement efficiently in
practice.
I've not looked at it. Any ideas?
Linus
next prev parent reply other threads:[~2002-11-08 17:51 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <3FAD1088D4556046AEC48D80B47B478C0101F4E7@usslc-exch-4.slc.unisys.com>
2002-11-08 3:51 ` [Linux-ia64] reader-writer livelock problem William Lee Irwin III
2002-11-08 17:13 ` Jeremy Fitzhardinge
2002-11-08 17:25 ` Linus Torvalds
2002-11-08 17:28 ` Linus Torvalds
2002-11-08 17:38 ` Jeremy Fitzhardinge
2002-11-08 17:43 ` David Howells
2002-11-08 17:57 ` Linus Torvalds [this message]
2002-11-09 2:48 ` Rusty Russell
2002-11-09 4:36 ` William Lee Irwin III
[not found] ` <3DCFDAE9.6D359448@email.mot.com>
2002-11-11 19:22 ` David Mosberger
2002-11-12 1:39 ` your mail Rik van Riel
2002-11-08 17:34 ` [Linux-ia64] reader-writer livelock problem David Howells
2002-11-08 17:54 ` David Howells
2002-11-08 17:55 ` Stephen Hemminger
2002-11-08 17:41 Van Maren, Kevin
2002-11-08 17:52 ` Matthew Wilcox
2002-11-08 18:05 Van Maren, Kevin
2002-11-08 19:19 ` Matthew Wilcox
2002-11-08 19:26 ` David Mosberger
2002-11-08 20:17 Van Maren, Kevin
2002-11-08 20:39 ` Matthew Wilcox
2002-11-08 20:24 Van Maren, Kevin
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