Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750930AbVLOTAp (ORCPT ); Thu, 15 Dec 2005 14:00:45 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750932AbVLOTAp (ORCPT ); Thu, 15 Dec 2005 14:00:45 -0500 Received: from gateway-1237.mvista.com ([12.44.186.158]:27381 "EHLO hermes.mvista.com") by vger.kernel.org with ESMTP id S1750929AbVLOTAp (ORCPT ); Thu, 15 Dec 2005 14:00:45 -0500 Message-ID: <43A1BD61.5070409@mvista.com> Date: Thu, 15 Dec 2005 11:00:49 -0800 From: David Singleton User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.8) Gecko/20050513 Fedora/1.7.8-2 X-Accept-Language: en-us, en MIME-Version: 1.0 To: dino@in.ibm.com Cc: linux-kernel@vger.kernel.org, Ingo Molnar , robustmutexes@lists.osdl.org Subject: Re: Recursion bug in -rt References: <20051214223912.GA4716@in.ibm.com> In-Reply-To: <20051214223912.GA4716@in.ibm.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3505 Lines: 110 Dinakar, after further testing and investigation I believe you original assessment was correct. The problem you are seeing is not a library problem. The changes to down_futex need to be reverted. There is a new patch at http://source.mvista.com/~dsingleton/patch-2.6.15-rc5-rt2-rf2. that reverts the changes to down_futex. Thanks for testing this. David Dinakar Guniguntala wrote: >Hi David, > >I hit this bug with -rt22-rf11 > >========================================== >[ BUG: lock recursion deadlock detected! | >------------------------------------------ >already locked: [f7abbc94] {futex} >.. held by: testpi-3: 4595 [f7becdd0, 59] >... acquired at: futex_wait_robust+0x142/0x1f3 >------------------------------ >| showing all locks held by: | (testpi-3/4595 [f7becdd0, 59]): >------------------------------ > >#001: [f7abbc94] {futex} >... acquired at: futex_wait_robust+0x142/0x1f3 > >-{current task's backtrace}-----------------> > [] dump_stack+0x1e/0x20 (20) > [] check_deadlock+0x2d7/0x334 (44) > [] task_blocks_on_lock+0x2c/0x224 (36) > [] __down_interruptible+0x37c/0x95d (160) > [] down_futex+0xa3/0xe7 (40) > [] futex_wait_robust+0x142/0x1f3 (72) > [] do_futex+0x9a/0x109 (40) > [] sys_futex+0x112/0x11e (68) > [] sysenter_past_esp+0x54/0x75 (-8116) >------------------------------ >| showing all locks held by: | (testpi-3/4595 [f7becdd0, 59]): >------------------------------ > >#001: [f7abbc94] {futex} >... acquired at: futex_wait_robust+0x142/0x1f3 > >--------------------------------------------------------------------- > >futex.c -> futex_wait_robust > > if ((curval & FUTEX_PID) == current->pid) { > ret = -EAGAIN; > goto out_unlock; > } > >rt.c -> down_futex > > if (!owner_task || owner_task == current) { > up(sem); > up_read(¤t->mm->mmap_sem); > return -EAGAIN; > } > >I noticed that both the above checks below have been removed in your >patch. I do understand that the futex_wait_robust path has been >made similar to the futex_wait path, but I think we are not taking >PI into consideration. Basically it looks like we still need to check >if the current task has become owner. or are we missing a lock somewhere ? > >I added the down_futex check above and my test has been >running for hours without the oops. Without this check it >used to oops within minutes. > >Patch that works for me attached below. Thoughts? > > -Dinakar > > > > >------------------------------------------------------------------------ > >Index: linux-2.6.14-rt22-rayrt5/kernel/rt.c >=================================================================== >--- linux-2.6.14-rt22-rayrt5.orig/kernel/rt.c 2005-12-15 02:15:13.000000000 +0530 >+++ linux-2.6.14-rt22-rayrt5/kernel/rt.c 2005-12-15 02:18:29.000000000 +0530 >@@ -3001,7 +3001,7 @@ > * if the owner can't be found return try again. > */ > >- if (!owner_task) { >+ if (!owner_task || owner_task == current) { > up(sem); > up_read(¤t->mm->mmap_sem); > return -EAGAIN; > > - 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/