Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753765AbZIAKFW (ORCPT ); Tue, 1 Sep 2009 06:05:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753585AbZIAKFV (ORCPT ); Tue, 1 Sep 2009 06:05:21 -0400 Received: from e23smtp05.au.ibm.com ([202.81.31.147]:48191 "EHLO e23smtp05.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753507AbZIAKFU (ORCPT ); Tue, 1 Sep 2009 06:05:20 -0400 Date: Tue, 1 Sep 2009 15:35:13 +0530 From: "K.Prasad" To: Jiri Slaby Cc: akpm@linux-foundation.org, mingo@redhat.com, linux-kernel@vger.kernel.org, Alan Stern , Frederic Weisbecker Subject: Re: [PATCH 1/1] hw_breakpoints: fix locking in load_debug_registers Message-ID: <20090901100513.GA3545@in.ibm.com> Reply-To: prasad@linux.vnet.ibm.com References: <1251756098-22852-1-git-send-email-jirislaby@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1251756098-22852-1-git-send-email-jirislaby@gmail.com> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3228 Lines: 87 On Tue, Sep 01, 2009 at 12:01:38AM +0200, Jiri Slaby wrote: > load_debug_registers is called with interrupts disabled from > many contexts and causes a warning to be dropped, e.g.: > ------------[ cut here ]------------ > WARNING: at kernel/softirq.c:143 local_bh_enable_ip+0x75/0xa0() > Hardware name: To Be Filled By O.E.M. > Modules linked in: nfs lockd auth_rpcgss sunrpc ath5k ath > Pid: 15083, comm: pm-suspend Tainted: G W 2.6.31-rc7-mm1_64 #687 > Call Trace: > [] warn_slowpath_common+0x78/0xb0 > [] warn_slowpath_null+0xf/0x20 > [] local_bh_enable_ip+0x75/0xa0 > [] _spin_unlock_bh+0xf/0x20 > [] load_debug_registers+0x51/0x60 > [] restore_processor_state+0x1b3/0x240 > [] acpi_suspend_enter+0x56/0xaf > [] suspend_devices_and_enter+0x14d/0x1a0 > [] enter_state+0xdb/0xf0 > [] state_store+0x91/0x100 > [] kobj_attr_store+0x17/0x20 > [] sysfs_write_file+0xe0/0x160 > [] vfs_write+0xb8/0x1b0 > [] ? do_page_fault+0x185/0x350 > [] sys_write+0x4c/0x80 > [] system_call_fastpath+0x16/0x1b > ---[ end trace fc3dd2304adb23aa ]--- > > Fix it by switching from spin_lock_bh to spin_lock_irqsave and > removing nested local_irq_save. > > Signed-off-by: Jiri Slaby > Cc: Alan Stern > Cc: K.Prasad > Cc: Frederic Weisbecker > --- > kernel/hw_breakpoint.c | 6 ++---- > 1 files changed, 2 insertions(+), 4 deletions(-) > > diff --git a/kernel/hw_breakpoint.c b/kernel/hw_breakpoint.c > index c1f64e6..bc5368d 100644 > --- a/kernel/hw_breakpoint.c > +++ b/kernel/hw_breakpoint.c > @@ -80,17 +80,15 @@ void load_debug_registers(void) > unsigned long flags; > struct task_struct *tsk = current; > > - spin_lock_bh(&hw_breakpoint_lock); > + spin_lock_irqsave(&hw_breakpoint_lock, flags); > > /* Prevent IPIs for new kernel breakpoint updates */ > - local_irq_save(flags); > arch_update_kernel_hw_breakpoint(NULL); > - local_irq_restore(flags); > > if (test_tsk_thread_flag(tsk, TIF_DEBUG)) > arch_install_thread_hw_breakpoint(tsk); > > - spin_unlock_bh(&hw_breakpoint_lock); > + spin_unlock_irqrestore(&hw_breakpoint_lock, flags); > } > > /* > -- > 1.6.3.3 > Hi Jiri, The above patch would cause a lock-dependancy warning since 'hw_breakpoint_lock' would be acquired with different levels of protection - spin_lock_irqsave() here and spin_lock_bh() [as Frederic pointed out that issue here: http://lkml.org/lkml/2009/7/27/466. The solution is to change the lock to spin_lock_irqsave() in all instances. I would be sending a patch shortly to that effect, along with a few other bug fixes. Thank you for your interest in fixing this! -- K.Prasad -- 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/