Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757563Ab3EYR4G (ORCPT ); Sat, 25 May 2013 13:56:06 -0400 Received: from mx1.redhat.com ([209.132.183.28]:15007 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757437Ab3EYR4D (ORCPT ); Sat, 25 May 2013 13:56:03 -0400 Message-ID: <51A0FB23.3050301@redhat.com> Date: Sat, 25 May 2013 13:55:47 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130514 Thunderbird/17.0.6 MIME-Version: 1.0 To: Manfred Spraul CC: LKML , Andrew Morton , Davidlohr Bueso , hhuang@redhat.com, Linus Torvalds Subject: Re: [PATCH v2] ipc/sem.c: fix lockup, restore FIFO behavior References: <1369495011-2586-1-git-send-email-manfred@colorfullife.com> In-Reply-To: <1369495011-2586-1-git-send-email-manfred@colorfullife.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1694 Lines: 44 On 05/25/2013 11:16 AM, Manfred Spraul wrote: > The double coward solution: > - wakeup stays FIFO > - fast switch back to per-semaphore spinlock mode > > The patch > a) fixes a lockup due to a missing restart. > b) makes the wakeups again FIFO (as linux <= 3.0.9) > c) tries to limit the time while in global lock mode as much > as possible. (same as linux-3.0.10-rc1) > > Changes: > - the wait-for-zero operations are moved into seperate lists. Thus they can > be checked seperately, without rescanning the whole queue. > - If a complex operation must sleep, then all pending change operations are > moved into the global queue. This allows to keep everything FIFO. > - When all complex operations have completed, the simple ops are moved > back into the per-semaphore queues. > > Advantage: > - FIFO. Dropping FIFO is a user visible change, and I'm a coward. I am still not entirely convinced that FIFO is worthwhile, but the code looks correct to me. Acked-by: Rik van Riel > - simpler check_restart logic. > - Efficient handling of wait-for-zero semops, both simple and complex. > - Fewer restarts in update_queue(), because pending wait-for-zero do not > force a restart anymore. > > Other changes: > - try_atomic_semop() also performs the semop. Thus rename the function. > > It passes tests with qemu, but not boot-tested due to EFI problems. > > Signed-off-by: Manfred Spraul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/