Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751378Ab2FMEcS (ORCPT ); Wed, 13 Jun 2012 00:32:18 -0400 Received: from mail-pz0-f52.google.com ([209.85.210.52]:60311 "EHLO mail-pz0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750886Ab2FMEcQ (ORCPT ); Wed, 13 Jun 2012 00:32:16 -0400 Date: Tue, 12 Jun 2012 21:31:45 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Mike Galbraith cc: paulmck@linux.vnet.ibm.com, LKML , Miklos Szeredi Subject: Re: rcu: endless stalls In-Reply-To: <1339558508.7472.26.camel@marge.simpson.net> Message-ID: References: <1339409176.7350.26.camel@marge.simpson.net> <20120611133953.GI2425@linux.vnet.ibm.com> <1339424543.7350.101.camel@marge.simpson.net> <1339435214.7358.43.camel@marge.simpson.net> <20120611180112.GD2521@linux.vnet.ibm.com> <1339438242.7358.62.camel@marge.simpson.net> <1339558508.7472.26.camel@marge.simpson.net> User-Agent: Alpine 2.00 (LSU 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2088 Lines: 54 On Wed, 13 Jun 2012, Mike Galbraith wrote: > On Mon, 2012-06-11 at 20:10 +0200, Mike Galbraith wrote: > > On Mon, 2012-06-11 at 11:01 -0700, Paul E. McKenney wrote: > > > > > 2aa15890 - mm: prevent concurrent unmap_mapping_range() on the same inode > > > > > > I confess, you lost me on this one. You believe that this commit is > > > the cause of the RCU CPU stall warnings? > > > > 4096 tasks on 4096 CPUs exit (well, try to) simultaneously. > > > > Call Trace: > > __mutex_lock_slowpath+0x94/0x150 > > mutex_lock+0x1a/0x40 > > unlink_file_vma+0x3f/0xf0 > > free_pgtables+0x40/0x100 > > exit_mmap+0xb0/0x120 > > mmput+0x49/0x120 > > exit_mm+0x122/0x160 > > do_exit+0x179/0x8d0 > > do_group_exit+0x3d/0xb0 > > sys_exit_group+0x12/0x20 > > > > Monster box dies screaming. > > That commit landed in stable, box with way too many cores (NR_CPUS=0!!) > chokes instantly with loads of spinners. Ok, so zillion CPUs grabbing a > mutex in lockstep is a bad idea (_having_ zillion?), but is there pilot > error involved in a logjam like this? Surely some mistake... I can't find any mention of which kernel release you're talking about. But Miklos's 2aa15890 unmap_mutex was introduced in 2.6.38 and removed in 3.0, when PeterZ converted i_mmap_lock to i_mmap_mutex, and removed the need for the additional unmap_mutex. The unmap_mutex would never have been taken in unlink_file_vma(), shown in your stacktrace above: it was for truncation and invalidation. The likely mutex in unlink_file_vma() would be the i_mmap_mutex. So I expect you're talking about a 3.0 or later kernel. But then why would someone "backport" Miklos's patch to stable for it? You lost me too! Hugh -- 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/