Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753725Ab3CZRf7 (ORCPT ); Tue, 26 Mar 2013 13:35:59 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:38557 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753629Ab3CZRf4 (ORCPT ); Tue, 26 Mar 2013 13:35:56 -0400 Message-ID: <5151DBD3.6080201@oracle.com> Date: Tue, 26 Mar 2013 13:33:07 -0400 From: Sasha Levin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130310 Thunderbird/17.0.4 MIME-Version: 1.0 To: Rik van Riel CC: torvalds@linux-foundation.org, davidlohr.bueso@hp.com, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, hhuang@redhat.com, jason.low2@hp.com, walken@google.com, lwoodman@redhat.com, chegu_vinod@hp.com, "Paul E. McKenney" , Andrew Morton Subject: Re: ipc,sem: sysv semaphore scalability References: <1363809337-29718-1-git-send-email-riel@surriel.com> In-Reply-To: <1363809337-29718-1-git-send-email-riel@surriel.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Source-IP: ucsinet22.oracle.com [156.151.31.94] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1757 Lines: 50 On 03/20/2013 03:55 PM, Rik van Riel wrote: > This series makes the sysv semaphore code more scalable, > by reducing the time the semaphore lock is held, and making > the locking more scalable for semaphore arrays with multiple > semaphores. Hi Rik, Another issue that came up is: [ 96.347341] ================================================ [ 96.348085] [ BUG: lock held when returning to user space! ] [ 96.348834] 3.9.0-rc4-next-20130326-sasha-00011-gbcb2313 #318 Tainted: G W [ 96.360300] ------------------------------------------------ [ 96.361084] trinity-child9/7583 is leaving the kernel with locks still held! [ 96.362019] 1 lock held by trinity-child9/7583: [ 96.362610] #0: (rcu_read_lock){.+.+..}, at: [] SYSC_semtimedop+0x1fb/0xec0 It seems that we can leave semtimedop without releasing the rcu read lock. I'm a bit confused by what's going on in semtimedop with regards to rcu read lock, it seems that this behaviour is actually intentional? rcu_read_lock(); sma = sem_obtain_object_check(ns, semid); if (IS_ERR(sma)) { if (un) rcu_read_unlock(); error = PTR_ERR(sma); goto out_free; } When I've looked at that it seems that not releasing the read lock was (very) intentional. After that, the only code path that would release the lock starts with: if (un) { ... So we won't release the lock at all if un is NULL? Thanks, Sasha -- 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/