From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C9B63C46460 for ; Thu, 9 Aug 2018 17:32:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8EDDE21EFC for ; Thu, 9 Aug 2018 17:32:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8EDDE21EFC Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=fieldses.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732658AbeHIT6i (ORCPT ); Thu, 9 Aug 2018 15:58:38 -0400 Received: from fieldses.org ([173.255.197.46]:48832 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730839AbeHIT6h (ORCPT ); Thu, 9 Aug 2018 15:58:37 -0400 Received: by fieldses.org (Postfix, from userid 2815) id CD5C81E3A; Thu, 9 Aug 2018 13:32:45 -0400 (EDT) Date: Thu, 9 Aug 2018 13:32:45 -0400 From: "J. Bruce Fields" To: NeilBrown Cc: Jeff Layton , Alexander Viro , Martin Wilck , linux-fsdevel@vger.kernel.org, Frank Filz , linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/5 - V2] locks: avoid thundering-herd wake-ups Message-ID: <20180809173245.GM23873@fieldses.org> References: <153378012255.1220.6754153662007899557.stgit@noble> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <153378012255.1220.6754153662007899557.stgit@noble> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I think there's also a problem with multiple tasks sharing the same lock owner. So, all locks are exclusive locks for the same range. We have four tasks. Tasks 1 and 4 share the same owner, the others' owners are distinct. - Task 1 gets a lock. - Task 2 gets a conflicting lock. - Task 3 gets another conflicting lock. So now we the tree is 3->2->1. - Task 1's lock is released. - Before task 2 is scheduled, task 4 acquires a new lock. - Task 2 waits on task 4's lock, we now have 3->2->4. Task 3 shouldn't be waiting--the lock it's requesting has the same owner as the lock task 4 holds--but we fail to wake up task 3. --b.