From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757100Ab0CJUeU (ORCPT ); Wed, 10 Mar 2010 15:34:20 -0500 Received: from gir.skynet.ie ([193.1.99.77]:59505 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755782Ab0CJUeS (ORCPT ); Wed, 10 Mar 2010 15:34:18 -0500 Date: Wed, 10 Mar 2010 20:34:01 +0000 From: Mel Gorman To: Andrew Morton Cc: linux-kernel@vger.kernel.org, Neil Horman , Andi Kleen , "Paul E. McKenney" Subject: Re: mmotm 2010-03-09-19-15: Lot of scheduling while atomic warnings related to RCU Message-ID: <20100310203401.GA14715@csn.ul.ie> References: <201003100342.o2A3gKvA022440@imap1.linux-foundation.org> <20100310195745.GP4883@csn.ul.ie> <20100310122138.a7da6f65.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20100310122138.a7da6f65.akpm@linux-foundation.org> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 10, 2010 at 12:21:38PM -0800, Andrew Morton wrote: > On Wed, 10 Mar 2010 19:57:46 +0000 > Mel Gorman wrote: > > > On Tue, Mar 09, 2010 at 07:16:03PM -0800, akpm@linux-foundation.org wrote: > > > The mm-of-the-moment snapshot 2010-03-09-19-15 has been uploaded to > > > > > > http://userweb.kernel.org/~akpm/mmotm/ > > > > > > and will soon be available at > > > > > > git://zen-kernel.org/kernel/mmotm.git > > > > > > It contains the following patches against 2.6.34-rc1: > > > > > > > With preempt and sleeping spinlock debugging on, I'm seeing a lot of warnings > > about scheduling while atomic. Starts off with messages like > > > > [ 0.572278] BUG: scheduling while atomic: swapper/1/0x00000002 > > [ 0.576004] 1 lock held by swapper/1: > > [ 0.580002] #0: (rcu_read_lock){.+.+.+}, at: [] kobject_uevent_env+0x363/0x4d0 > > [ 0.600001] Modules linked in: > > [ 0.608003] Pid: 1, comm: swapper Not tainted 2.6.34-rc1-mm1-vanilla #1 > > [ 0.612001] Call Trace: > > [ 0.616005] [] ? __debug_show_held_locks+0x22/0x24 > > [ 0.620005] [] __schedule_bug+0x77/0x7c > > [ 0.624004] [] schedule+0xcc/0x723 > > [ 0.628003] [] schedule_timeout+0x2d/0x28d > > [ 0.632003] [] ? mark_held_locks+0x4d/0x6b > > [ 0.636004] [] ? _raw_spin_unlock_irq+0x30/0x5d > > [ 0.640003] [] ? trace_hardirqs_on_caller+0x110/0x134 > > [ 0.644003] [] wait_for_common+0xdc/0x152 > > [ 0.648003] [] ? default_wake_function+0x0/0x14 > > [ 0.652004] [] wait_for_completion+0x1d/0x1f > > [ 0.656004] [] call_usermodehelper_exec+0xad/0xfa > > [ 0.660004] [] ? prepare_usermodehelper_creds+0x136/0x168 > > [ 0.664003] [] kobject_uevent_env+0x44a/0x4d0 > > [ 0.668003] [] ? kobject_uevent_env+0x363/0x4d0 > > [ 0.672003] [] kobject_uevent+0xb/0xd > > [ 0.676002] [] kset_register+0x37/0x3f > > [ 0.680004] [] bus_register+0x11f/0x2b1 > > [ 0.684005] [] platform_bus_init+0x2c/0x44 > > [ 0.688003] [] driver_init+0x1d/0x29 > > [ 0.692004] [] kernel_init+0x12e/0x1e3 > > [ 0.696003] [] kernel_thread_helper+0x4/0x10 > > [ 0.700004] [] ? restore_args+0x0/0x30 > > [ 0.704003] [] ? kernel_init+0x0/0x1e3 > > [ 0.708002] [] ? kernel_thread_helper+0x0/0x10 > > > > There are a lot of warnings along these lines during boot. This system did > > boot *eventually* but it was in obvious trouble. The warnings appear to > > be all around kobject_uevent_env acquiring the RCU lock and then going to > > sleep. Most likely candidate problem patches in mmotm are > > > > sysctl-fix-up-remaining-references-to-uevent_helper > > sysctl-fix-up-remaining-references-to-uevent_helper-fix > > > > But there are also a whole host of other sysctl-related changes around RCU in > > there. The changelog implies that these patches are part of some long-lived > > review process so I didn't delve too deeply. The people most likely to be > > involved based on comments in the changelog are cc'd. > > > > Thanks. It's Neil's > sysctl-fix-up-remaining-references-to-uevent_helper-fix.patch which does > > --- a/lib/kobject_uevent.c~sysctl-fix-up-remaining-references-to-uevent_helper-fix > +++ a/lib/kobject_uevent.c > @@ -273,10 +273,11 @@ int kobject_uevent_env(struct kobject *k > #endif > > /* call uevent_helper, usually only enabled during early boot */ > + rcu_read_lock(); > helper = rcu_dereference(uevent_helper); > if (helper[0]) > retval = uevent_call_helper(subsystem, env); > - > + rcu_read_unlock(); > exit: > kfree(devpath); > kfree(env); > > Indeed, I spotted that but the large number of dependencies around it made me wonder was it really that patch or a problem with the whole thing. I confess I didn't actually look to see what they were doing. Shortly after I sent the first mail, I removed all these patches from the series just so it would boot without crapping all over the console. > Ho hum. I guess all of > > #rcu-add-rcustring-adt-for-rcu-protected-strings.patch: TBU > rcu-add-rcustring-adt-for-rcu-protected-strings.patch > #add-a-kernel_address-that-works-for-data-too.patch: TBU > add-a-kernel_address-that-works-for-data-too.patch > sysctl-add-proc_rcu_string-to-manage-sysctls-using-rcu-strings.patch > sysctl-use-rcu-strings-for-core_pattern-sysctl.patch > sysctl-add-call_usermodehelper_cleanup.patch > sysctl-convert-modprobe_path-to-proc_rcu_string.patch > sysctl-convert-poweroff_command-to-proc_rcu_string.patch > #sysctl-convert-hotplug-helper-string-to-proc_rcu_string.patch: jirislaby crash > sysctl-convert-hotplug-helper-string-to-proc_rcu_string.patch > #sysctl-use-rcu-protected-sysctl-for-ocfs-group-add-helper.patch: Joel nack > sysctl-use-rcu-protected-sysctl-for-ocfs-group-add-helper.patch > # > sysctl-fix-up-remaining-references-to-uevent_helper.patch > sysctl-fix-up-remaining-references-to-uevent_helper-fix.patch > # > sysctl-clean-up-vm-related-variable-declarations.patch > sysctl-clean-up-vm-related-variable-declarations-fix.patch > # > sysctl-remove-references-to-ctl_unnumbered-which-has-been-removed.patch > # > # > sysctl-extern-cleanup-c_a_d.patch > sysctl-extern-cleanup-signal.patch > sysctl-extern-cleanup-binfmts.patch > sysctl-extern-cleanup-pid.patch > sysctl-extern-cleanup-mm.patch > sysctl-extern-cleanup-compat.patch > sysctl-extern-cleanup-latencytop.patch > sysctl-extern-cleanup-file-nr.patch > sysctl-extern-cleanup-rcu.patch > sysctl-extern-cleanup-block-iopoll.patch > sysctl-extern-cleanup-module.patch > sysctl-extern-cleanup-sg.patch > sysctl-extern-cleanup-acct.patch > sysctl-extern-cleanup-rtmutex.patch > sysctl-extern-cleanup-lockdep.patch > sysctl-extern-cleanup-poll.patch > # > kmod-add-init-function-to-usermodehelper.patch > kmod-add-init-function-to-usermodehelper-fix.patch > kmod-replace-call_usermodehelper_pipe-with-use-of-umh-init-function-and-resolve-limit.patch > kmod-replace-call_usermodehelper_pipe-with-use-of-umh-init-function-and-resolve-limitcleanup.patch > > are not a prospect for 2.6.34. There are issues in the rcustring > patches and the others have dependencies. I suppose I can rebase > sysctl-extern-cleanup-* though. > -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab