From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id 781E16B0044 for ; Thu, 29 Jan 2009 03:35:48 -0500 (EST) Date: Thu, 29 Jan 2009 09:31:08 +0100 From: Oleg Nesterov Subject: Re: [RFC v7] wait: prevent exclusive waiter starvation Message-ID: <20090129083108.GA27495@redhat.com> References: <20090123095904.GA22890@cmpxchg.org> <20090123113541.GB12684@redhat.com> <20090123133050.GA19226@redhat.com> <20090126215957.GA3889@cmpxchg.org> <20090127032359.GA17359@redhat.com> <20090127193434.GA19673@cmpxchg.org> <20090127200544.GA28843@redhat.com> <20090128091453.GA22036@cmpxchg.org> <20090129044227.GA5231@redhat.com> <20090128233734.81d8004a.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090128233734.81d8004a.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org To: Andrew Morton Cc: Johannes Weiner , Chris Mason , Peter Zijlstra , Matthew Wilcox , Chuck Lever , Nick Piggin , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Ingo Molnar , stable@kernel.org List-ID: On 01/28, Andrew Morton wrote: > > On Thu, 29 Jan 2009 05:42:27 +0100 Oleg Nesterov wrote: > > > On 01/28, Johannes Weiner wrote: > > > > > > Add abort_exclusive_wait() which removes the process' wait descriptor > > > from the waitqueue, iff still queued, or wakes up the next waiter > > > otherwise. It does so under the waitqueue lock. Racing with a wake > > > up means the aborting process is either already woken (removed from > > > the queue) and will wake up the next waiter, or it will remove itself > > > from the queue and the concurrent wake up will apply to the next > > > waiter after it. > > > > > > Use abort_exclusive_wait() in __wait_event_interruptible_exclusive() > > > and __wait_on_bit_lock() when they were interrupted by other means > > > than a wake up through the queue. > > > > Imho, this all is right, and this patch should replace > > lock_page_killable-avoid-lost-wakeups.patch (except for stable tree). > > I dropped lock_page_killable-avoid-lost-wakeups.patch a while ago. > > So I think we're saying that > lock_page_killable-avoid-lost-wakeups.patch actually did fix the bug? I think yes, > And that "[RFC v7] wait: prevent exclusive waiter starvation" fixes it > as well, and in a preferable manner, but not a manner which we consider > suitable for -stable? (why?) I meant that lock_page_killable-avoid-lost-wakeups.patch is much simpler, and thus it looks more "safe" for -stable. But it is not optimal, and Johannes's patch is also more generic, it fixes wait_event_interruptible_exclusive() as well. > And hence that lock_page_killable-avoid-lost-wakeups.patch is the > appropriate fix for -stable? > > If so, that's a bit unusual, and the -stable maintainers may choose to > take the patch which we're putting into 2.6.29. Well, I don't know ;) But Johannes's looks good to me, if you already dropped the old patch, then I think this one can go into -stable after some testing. Hopefully maintainers can review it. Oleg. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org